I can tell you a few of his mods since I have then also:
Dominos for action bar control( lets you move em, and shrink em)
Titan Panel for the top bar(you can put location, experience,mail, all kinds of stuff on it)
perl unit Frames gives the player and party frames (so you can move em, shrink em, etc.)
Those are the biggies that let you move and shrink your bars to make more room.
Some of the others I know we both use are mailget, questhelper, auctioneer,ATSW.
I also have Atlas and Atlas loot enhanced for the instance maps and loot tables.
BTW he also has a 22" widescreen monitor. That also makes for lots of room.