Someone asked for a list of the addons I've been using in classic. Both Curse and WowInterface have classic addons segregated from the retail ones, if you use the Twitch client for updating there's a dropdown list in the upper right for choosing which addons you're updating. (I'm not sure how Minion works, but I presume it has a setting for them as well.) You can use the "Get More Addons" list to get addons, and it will get the ones for the version you're looking at.
I'll list them in alphabetical order, with a few comments.
AdvancedInterfaceOptions--Gives you additional control over the CVARs in your interface. Kind of a niche addon you may not need.
AtlasLootClassic--what drops from what boss, crafting recipes, etc. Also, I suppose, useful if you really, really need to be able to link Thunderfury, Blessed Blade of the Windseeker.
Bagnon--All your bags in one frame.
Bartender4--Same addon I use in retail, lets you easily position your action bars, set keys, hide bars, etc.
BasicComboPoints--mostly for rogues, puts your combo points in a number right in the center of your screen.
Better Vendor Price--puts in the tooltip what the item you are mousing over sells for at the vendor. Computes for the stack you have, as well as a full stack. There's 2 or 3 addons like this, I liked the fact that it did the stack computations for me.
BigWigs--you may prefer DBM.
BugGrabber--works with BugSack below, mostly of interest if you debug addons.
BugSack--works with BugGrabber above...yeah.
DejaClassicStats--adds to the character info pane other information you might want to know. If you're obsessive.
ElkGuild--(the r24-alpha version works with classic) Gives a nice display of the guild members online as well as all their notes in one clickable, easy to read format.
IceHud--Sadly, I haven't gotten all of this to work yet. I really like the ability to see health and mana in the center of the screen, but it's not quite right yet.
LittleWigs--the dungeon version of BigWigs. If you use DBM it has something else.
MapCoords--for those cases where you're hunting for a spot you've read about.
MaxCam--lets you scroll out the camera.
OmniCC--shows cooldowns on buttons in nice clear numbers.
oRA3--Helps out the raid leader. )
Perl Classic Unit Frames--replaces the unit frames. On Retail I use Z-perl, but this is the one that was updated for classic. Makes it easier to display what I want on the frames, I like health as well as percentage.
Plater Nameplates--while I like TidyPlates better, this is updated for Classic and Tidy isn't.
Quartz--Lets me put casting bars where I'm used to them, so I can interrupt what I mean to. Sometimes.
Raven--Put buff and debuff bars where I want them, with text so I don't have to remember what the icon means.
Real Mob Health--Classic doesn't put the same info in the combat log about mob health. This tracks what you fight and records its health so it doesn't just show as 100 percent but you can see what that means. Very useful in judging if a 50 point special attack is going to kill the thing or not. Integrates seamlessly with the other addons mentioned.
Recap--In game dps and healing meter. Some people prefer Details, this is the one I use on retail as well. It's simple, and easy to put the raid dps in one spot.
Titan Panel Classic--the forerunner of the Broker system in use currently. Puts info along the top of the screen like cash, durability, etc. Not all the broker addons have been updated, so while I've experimented with Chocolate Bar/Broker addons this has worked better.
Titan Panel Classic [Guild]--an alternative to ElkGuild.
VuhDo--The same addon I use for healing in retail. Pretty much same options.
WeakAuras2--I've actually not set up any in classic yet. I should.
WIM (WoW Instant Messenger)--pops whispers up in their own box, and allows you to keep a history. Very nice messaging app.