When I started this blog, though, I committed myself to trying to do an update every week day, at least. Since "three bubbles on the XP bar" really isn't much of an update, though, I figured I'd talk about addons.
I played WoW for a good long while before I started messing about with addons... and for the longest time, there were only a couple that I installed. Those are still pretty important core addons for all my characters.
Lightheaded is a wonderful addon that gives you an extra pane in the quest log window... a pane full of information about the quest you are looking at. It includes information like where you need to go to turn in the quest, and comments (sometimes pages and pages of comments) from WoWHead about the quest. Strategys for soloing difficult mobs, locations to find the particular critters you need to kill, advice on what to skip and what to make sure you do - it's all there. While you can do a lot of quests without consulting Lightheaded, it's especially invaluable for those old-world quests that tell you "Find Prester John", without mentioning to you that he's a hermit living in a cave on the other continent. Good stuff.
Lightheaded works extremely well with TomTom, an addon for managing waypoints and world-map markers (which they should, since they were both written by a truly talented chap who goes by the nom de plume of Cladhaire). Give TomTom some coordinates - say, from clicking on them in a Lightheaded entry - and TomTom will plop down a lil' green dot on the map for you. It also allows you to pick what you're next point of interest is, and provides a waypoint arrow that you can use to determine direction/distance to that point. It's actually a lot more capable than that, but it's most basic functions are all I use, and I like it.
Gatherer, as you may expect from the name, helps you gather. Ore, herbs, chests, clams, whatever - if you can find it lying around, gatherer can help you track it. The WoWHead DB is an addon that lets Gatherer know about tons of nodes that WoWHead users have already found and tracked, and if you're in a guild, you can set up Gatherer to share information about new nodes you find with your guildmates. It also comes with a heads-up display that you can use to help guide you to the next most likely node of whatever type you're interested in. I hardly ever use the HUD, though - I just find it too visually distracting.
As time went on, I started trying out more and more addons. Some stuck, some didn't. Some are purely cosmetic or otherwise not a big influence on actual game play. For example, I think AchievementSnap (screenshot your achievement moments), AutoProfit (automatically sell all grey items at a vendor), and DagAssist (seldom used trade and class skill drop-down menu) are nice, but they're hardly essential, and they really don't change the way I play the game at all.
That said, there are a couple of addons that - IMHO - really get the job done. They either make playing the game a more enjoyable experience, or make understanding the game easier (which makes it easier to play well) . In no particular order, they are:
EveryQuest. This gives you the ability to see information about... wait for it... every quest in the game. Integrates with Lightheaded, so you can also see that treasure trove of information as well. Couple this with the ability to sync with your realm server and figure out what quests you've completed, and track quest completion, and this is an absolute must-have addon if you're going for the Loremaster achievement. Because otherwise, you're going to be wandering around all of Kalimdor, trying to figure out where that last quest you need is...
Auctionator. Makes using the auction house about 1000% easier, particularly for dumping loads of goods into the market, and finding the best deals on whatever materials you happen to need at the moment.
Deadly Boss Mods. Picked this one up when I was hitting Naxx semi-regularly with my guild. If you're going to be running any sort of dungeon or raid, this is an essential addon... not that it tells you anything you couldn't pick up otherwise, really; but because it puts that information right in front of your face, so you don't miss in in the hustle and bustle of whatever fight you're doing at the moment.
Skada is actually my second-generation damage meter. I originally used Recount, but when I started playing a disc priest, I wanted something that would do a better job of tracking damage absorption stats. Even better from my point of view, Skada lets me set it up to show one view while in combat (threat) and another view out of combat (overall dps). While I don't care too much about that on my priest, it's a nice to have that bit of utility for my mage, and absolutely wonderful to have when tanking with Aeven.
Perfect Raid. Along with it's related addons, this is my raid frame addon of choice. It's from that Cladhaire fellow I mentioned above, and as with Lightheaded and TomTom, Perfect Raid does a wonderful job (for me, at least). Easy to configure, it will actually work right out of the box for a lot of people. I use it primarily for party and raid healing on my priest, but it's been useful when tanking with Aeven as well.
Quartz is a "modular casting bar", which I am pretty sure is Latin for "amazingly awesome". Seriously, go read the desription of what it does - or, ever better, install it and see what it does. I first started using it to show how latency was affecting spell casting - high latency means that I can actually start casting before the current spell cast ends (and in some cases, well before the current spell cast ends). It lets me make sure that, mana and cooldowns permitting, I've always gone something in the pipe, ready to burn a firey path of destruction towards whoever has annoyed me most in the past few seconds.
SexyCooldown is similar, but not the same, which is probably a bit confusing until you actually see it in action. It gives you one bar, but man, that's a nice bar to have. It shows you, graphically, where your cooldowns are. Toss off a judgement? You'll see an icon appear on the bar, sliding from right to left. It will move more and more quickly as the cooldown finishes, with a nice big icon pulse at the end to let you know "Hey, you can use this ability again right now!" With a bunch of abilities, you can glance at the bar and see "Ok, I can toss of a judgment now, then Exorcism will be up in a second or two, and I'll be able to pop a potion in about 30 seconds." Absolutely wonderfully awesome.
Finally... I save the best for last, or at least, the most controversial. GearScore. Yes, I have it installed. No, I don't make a big deal about it. When I started healing LFD pugs, though, I found out pretty quickly that it was a useful tool for me as a healer. If I saw a tank with a 2k gearscore in a heroic, I'd know right away that I'd have to pay more attention to them. If I saw a mage with a 6K gearscore, I'd know that they would probably be holding back to keep from pulling aggro, and that hitting them with a power infusion would be a waste. On any character below level 80, though, it's pretty much useless. So I generally just ignore it on Aeven.
There's a few more, but those are the main ones. If I was really pushed - if for some reason, I needed to cut back on my plugins - I think I'd really have to keep SexyCooldown, Quartz, Skada, Lightheaded, TomTom, and Perfect Raid. Maybe not in that exact order, though, depending on which character I was most interested in playing at the moment.