Some many good sites, so little space. Alas, that is the way it is but with so much information to chose from I can offer these links and built in cheat codes. Plus, this character editor which can be quite handy. I will add the list for the items and creatures soon.
As for the cheat codes, here they are:
In order to enable them, you have to edit your baldur.ini file in the Baldur's Gate directory.
Under the [Game Options] heading, put Cheats=1 (Case sensitive). The next time you play, press CTRL-TAB and a window will appear. The following codes will now work: (Note: Codes are case-sensitive.)
Moves the entire party to wherever the cursor is located
Creates an Item.
Creates a Creature. Only Use First 6 of Character Names.
Change Experience for All Members.
Puts three critical items in your inventory.
Adds 500 Gold.
Puts a CowKill scroll in inventory.
Creates a friendly Drizzt.
Creates a hostile Drizzt.
Removes Fog of War from Current Map.
Summons a bunch of berserk chickens.
Puts Healing Items in inventory.