Try ascension. It was developed by david gaider, one of the blokes who worked for bioware making BG. (though it should be made clear that it is not a bioware product, nor is the mod affiliated with bioware). It greatly modifies the TOB expansion, to try and achieve what they would have done if they did not have to work within the time limit that they had for making the expansion.
Despite being completely awesome, it also makes the endgame bosses much more difficult, so you might want to avoid it on your first playthrough.
I like the tactics mod as well (which essentially changes changes some battles and areas from "easy-normal" to "oh god why hath thee forsaken me", also not recommended for first playthrough).
And the Item's upgrade mod (which gives you OP items basically, but if you are using tactics and ascension and stuff it isn't that bad).
They aren't very lore accurate if you are concerned about that though.
You can get all those (ascension, tactics, and item upgrade, as well as some other mods) here
http://weidu.org/main.htmlI also recommend Unfinished Business, which puts many of the quests that the devs didn't have time to finish back in the game.
Their is also Tutu which lets you play BG1 in the BG2 engine, removing the XP cap, letting you use kits, and a better transition into BG2.
Alternately, you can use Baldur's gate trilogy (lets you play through BG1-BG2 in one game), which, although i haven't used, is apparently good as well.