1) Widescreen Mod
Sharper graphics on moderns LCDs. No additional GUI mod is needed, as IWD was designed with a more scalable interface than most other Infinity Engine releases.
2) Unfinished Business for Icewind Dale
Restores and finishes content cut from the original release, hence it blends with the original game perfectly. Stable, fun & professional.
3) Item Upgrade for Icewind Dale
Adds the ability to upgrade your equipment. Definitely fun for crafters!
4) Icewind Dale Fix Pack
NEW! This is split out from the Tweak Pack, which seems to no longer be available. Below are the notes for the old Tweak Pack, but it looks like this new Fix Pack just contains fixes only. I will update this post if I find a replacement for the tweak components.
Adds bugfixes, minor cosmetic tweaks, cheats, ruleset tweaks.
I recommend the following components:
Weapon Animation tweaks (less repetitive sword swinging animations)
Restore IWD Loading Screens (HIGHLY subjective. Most people won't care, but I prefer the original look of the pre-Trials of the Luremaster loading screens)
Icon Improvements (replaces some icons with their usually more detailed BG1, BG2 equivalents. Subjective, but subtle enough many won't even notice)
Force All Dialog to Pause (no more cheap shots from enemies attacking while are you chatting)
Personal Preference. If in doubt, skip.
Also very subjective. Some make the game closer to Pen and Paper and many are outright cheats. If in doubt, skip.
Convenience Tweaks and/or Cheats:
Higher HP on Level Up (may be worth it to first-timers. Ensures you don't get poor die rolls with IWD's random HP on level up system, which is based on a roll of the character's hit die)
Adds new items, spells, a quest, new creatures, new AI scripts and more. Can modify the feel of the game a bit, so I recommend holding off for a first-time playthrough. Works best if installed before the tweak pack. Overall very fun and high quality mod.
Icewind Dale NPCs
Don't want to make your own party? Check out these premade, chattering NPCs. Not ideal for tacticians and powergamers, perhaps, but if you want a bigger dose of roleplaying in IWD, this mod will make you happy. Best installed before Tweak Pack.
Full Plate & Packing Steel
Changes the AD&D 2e Armor rules so that light armors give you a better chance to dodge and heavy armors absorb damage. This is as opposed to heavy armors decreasing the chance you get hit.
Yes, D&D armor rules are strange. The most common justification I've heard for it is heavy armors gives you more "glancing blows" which don't do damage.
Opinions aside I haven't actually tested this last one, being accustomed to standard D&D rules. It may be interesting to try though. I'm also pretty sure this should be installed before the tweak pack, as usual. Be careful to note compatibility as some tweak pack components directly conflict.
As mentioned by chautemoc, there are a couple sites keeping comprehensive indexes of mods.
Pocket Plane Group Modlist
Sorcerer's Palace Modlist