Great thread, already thinking about trying some of those out for my mage!
By the way, Gatherer also indicates where you've found chests and schools of fish.
Outfitter is a very handy mod for switching gear, which I find essential on my druid as I can set up different sets of kit for healing / bear / cat which then automatically change when I shapeshift. I think it'd be useful for any class though, as it has options for riding (automatically equip Carrot on a Stick when mounted), Argent Dawn (automatically equip trinket when in the Plaguelands), around town (your sexy-looking but not-so-great gear), PVP and so on, as well as being able to set up custom sets.
Another one I use is CritLine, which tells you your record (both critical and non-critical) for every spell / attack you use. It stores this on a table accessible from an icon on the edge of the mini map, and can be set to automatically take a screenshot when you get a new personal best. It's not so much useful as fun really, but it's nice to know what the hardest you've ever hit something is :)
Also, KLH ThreatMeter is very useful, particularly in raiding, to show who is at the top of the threat list. Lets the dps know when to back off a bit and the tanks know when thay have to step it up. Only those with the mod installed show on the list I believe.
Auto Resurrect - does what it says. Handy because quite often people will go afk if they die when in a group to get a drink or something. This mod lets you automatically accept a resurrection from another player (not a spirit healer rez) so you can be healed, buffed and ready to go by the time you get back to your keyboard.
Edited, Nov 29th 2006 4:27pm by Rubytitania