Background: There are lots of mods available for the BG series of games, ranging from the essential bugfixes and tweaks, to "mega-mods" designed to introduce whole new areas full of quests and adventures.
I've played BGII(+ToB) a number of times - at least 5 parties through all of BGII, two parties through to the end of ToB too, but I've only tried BG I once and didn't get very far - partly because I played BG II first, and BG I's interface isn't quite as good, plus starting at level 1 is quite tricky after playing the high-powered characters of BG II.
Since then, though, clever people have created mods which convert BG I's content to run in the BG II engine. One is called "BG1tutu", which disables playing of BG II/ToB while playing BG I (BG II can be easily restored, though), and the other is called Baldur's Gate Trilogy, which allows all of BG I & II to be played. These mods allow for a number of improvements to the BG I experience - higher resolutions, better path-finding, TAB key to highlight doors and containers, ability to use BG II kits, etc. I've decided it's time to play BG I through using BGT, and to also install some of the mega-mods in addition to my usual collection. Some of the mods below would be useful even if you've never played a BG game before, some are only recommended once you've played through a reasonable amount of the game, and some are for expert players only, I'll try to explain which and describe why.
Start with clean installs of BG I and II :
1. Install BG I and Tales of the Sword Coast
a. If you have the original 6-disc set, also install the BG I patch
b. If you have the Original Saga 3-disc set, the patch is already included
2. Install BG II and Throne of Bhaal, then patch 26498 for BG II + ToB
(ToB is required for some of the mods below)
Then for the mods. The general order is BG2_Fixpack first, then the mega-mods, (and I believe any non-tutu/BGT mods for BG I go here).
Install BGT (which converts all of the BGI areas into BGII), then the BGT/tutu-compatible BGI mods.
Finally, install NPCs, other minor quests, and finally any small tweaks.
And then cross fingers and hope it all works !
|BG2_Fixpack-v3.exe||Essential every time you play, even the first. Squishes dozens if not hundreds of bugs, small and large, in quests, romances, items, spells, etc.|
|Mega-mods - probably only for use if you've played through the game a few times, and are quite experienced :|
|SoSv1.11.rar||Shadows over Soubar - adds new areas and quests and NPCs and stuff to BG II|
|TDDv1.11.rar||The Darkest Day - more new areas, quests, NPCs to BG II|
|(NeJ2v691.exe)||Never-Ending Journey - adds new areas, based on Icewind Dale I, to BG II - couldn't get this to install, it requires a different fixpack which isn't compatible with some of the other mods. Found out later I could have pochled the install file for it and made it work, but it was too late by then.|
|Ascension-WeiDU-v1.4.21.exe||Modifies the very end of Throne of Bhaal - possibly slightly harder than the standard ending (!)|
|BGT104_Install.rar||Baldur's Gate Trilogy - Converts BG I content and adds it in to your BG II game - good for experienced players, and also people who want to play BG I but are put off by the older interface.|
|SoBH206Full.rar||BG I mod - requires BGT/tutu - adds old AD&D module "L1 - The Secret of Bone Hill" (and most of L2, I believe)|
|BG1NPC4BGTWeiduv111.rar||Updates a number of BG I NPCs - improved dialogues, some mini-quests, etc. Needs BGT/tutu.|
|BPv177.rar||The Big Picture - modifies scripts, spells, and all sorts of bits and pieces to integrate the mega-mods better. I think.|
|BPv177_TOB_fix.rar||BP fix for ToB|
|BP_s_and_h_Patchv7.zip||patch for TBP, probably required.|
|BP-BGT-Worldmap-v6.5.rar||Updated world map - compatible with the mega-mods, and reqired to play them - otherwise some areas may be unreachable|
|Other major mods|
|eSeries-v1.8.exe||This gives you a set of improved scripts to control your characters.|
|gMinion-v1.8.exe||and this installs improved abilities for summoned monsters|
|Weimer-TacticsMod-v23.exe||Ahhh, Tactics. For experienced players only, and those that like a challenge. There are a few general fixes in here (e.g. a fix called "Slightly smarter mages and liches"), which work roughly as you'd expect. Then there are some fights which are "improved" (generally made more difficult), mainly by making the opponents much smarter and less likely to be defeated by standard "cheesey" tactics. For example, you start BG II in the Dungeon of Jon Irenicus (commonly known by BG players as "Chateau Irenicus" (CI)). In CI, there's a Duergar named Ilyich, who has a few other duergar as backup, mostly low-level fighters, one mage. This group is fairly easy to defeat even playing with a solo character - it might involve resting once or twice to heal/recover spells, but it's manageable. Improved Ilyich - for a start, you can't rest, because you keep getting ambushed by Rune Assasains. Ilyich has a few new friends - like high-level cleric named Zhivago who summons a Fallen Deva, a Neophyte Glabrezu, and a nasty mix of level-12 characters all intent on making your stay short and unpleasant. They can be beaten, but it requires use of everything your party has and clever tactics too - which is the point of this mod, I guess.|
|1pp-v2.exe||Mod by One Pixel Productions, which improves a number of the inventory icons used in the game (bases quite a few of them on either BG I or Icewind Dale versions, I think)|
|NPCs (all able to join your party)|
|Weimer-SolaufeinMod-v102.exe||Solaufein (a drow fighter/mage in Ust Natha in the Underdark) becomes an NPC who can join your party. Lots of extra dialogue, banter with party NPCs, romance option, and a couple of extra quests.|
|Weimer-Valen-v45.exe||Valen (a vampire fighter/thief in Bodhi's lair) becomes an NPC who can join your party.|
|tashia205g.zip||Tashia, a sorcerer, joinable NPC (with banters/quest/romance options)|
|KelseySoA||Kelsey, a sorcerer joinable NPC (with banters/quest/romance options)|
|KelseyTOB||ToB component for Kelsey|
|Other small mods - tweaks and improvements of various sorts|
|BagBonus v1.0.rar||adds a bag containing some useful items to "Chateau Irenicus".|
|ImprovedBAMs-v2.exe||improves some of the spell casting animations (borrows from Icewind Dale II)|
|Oversight-v10.exe||Contains fixes to alignments, classes and spells, among other things.|
|Scriptable_Spells-v1.4.exe||updates spells to be detectable by scripts and more usable in scripts|
|Sequencer_Memory-v1.2.exe||should allow you to remember what spell strategy you've used when creating sequencers/spell triggers|
|Weimer-ItemUpgrade-v35.exe||Gives Cromwell (BG2) and Cespenar (ToB) a whole new list of possible item upgrades, some of which are for simple convenience (e.g. combining Boots of Speed with some of the other types of boots), some are to "beef up" otherwise useless items (e.g. quiver of plenty +1 to +2/+3), and some are to add some new choices to "underrepresented" weapon types (e.g. clubs)|
|Weimer-Spell50-v6.exe||Normally, spell effects are capped at level 20, even if character level is higher. This extends spell effects to level 50 (for players and monsters too - watch out !)|
|Weimer-Underrep-v5.exe||Another mod introducing "underrepresented" items to the game - in this case a merchant appears with a wide range of daggers, staves, clubs, maces, bastard swords, etc.|
|PnPCelestials-v4.exe||By the time your characters can summon Devas and Planetars, they tend to be minced by the opposition. This mod toughens them up to make them more like the P'n'P versions.|
|BG2_Tweaks-v4.exe||A whole bunch of useful bits to make the game easier on any play through after the first (and one or two components even for the first), including unlimited item stacking (arrows, potions, scrolls, gems), and the most important - Shut Up "You Must Gather Your Party Before Going Forth" !|
|Setup_BG2SoAItemImportMod_v2.rar||Allows you to bring some items from BG I into BG II.|
|SetupGUI.exe (from BGT)||Updates the GUI and fixes the songlist.2da file to use BG I music.|
 BG I = Baldur's Gate I, ToTSC = Tales of the Sword Coast
 BG II = Baldur's Gate II : Shadows of Amn, ToB = Baldur's Gate II : Throne of Bhaal
In summary / disclaimer : These are the mods I'm using in my current game, however there's no guarantee that some combination of mods here doesn't clash in some way which will mess up the game later on. There are quite a lot of other mods I could have chosen, but it is a bit of a headache trying to find out which mods are compatible with each other (in general, mods which install using "Weidu" will be mostly compatible, because Weidu can be set up to patch/edit files rather than replacing them - but it needs a certain amount of care on the part of mod makers, and if two mods are modifying the same character or location, clashes can still occur).
Hopefully this will be useful to someone !