QuestHelper causes my computer to crash, too, so I use an addon called Carbonite. It’s like QuestHelper + Cartographer combined, so it’s pretty heavy on the memory usage (but you can get rid of Cartographer if you use it) plus a ton of other features. There’s a paid subscription version with even more features, but I find the free version is more than enough for me.
Other addons I use:
Atlas + Atlasloot – maps of all the dungeons and where each boss is, plus what possible loot is dropped along with percentages for each piece of loot. You can also use AtlasLoot to browse gear you can earn through the various reputations and the rep level required. PVP/Arena gear is also included.
RatingBuster – breaks out what all the stat points on each piece of gear mean for my character and compares equipment so I know what I’m gaining/losing for every possible replacement I look at.
Prat – color codes my chat box so I know the class and level of the person speaking in chat
Scrolling Combat Text – a lot more display and font options than the in-game combat text
IceHUD – I just like HUDs – no more staring at the upper left corner during fights, all the info I need is right there around my character, allowing me to be more aware of other things going on
Gatherer – tracks every resource node I find (and group/raid members, and guild members – you can even share data with people)
Auctioneer – remembers every auction you ever see, then gives you median prices so you have an idea of what things are worth when you find them. Can also search auctions for really good deals, and even breaks out stacks of items into cost-per-unit
Linkerator – allows me to generate a linked item in chat just by typing it out, without having the item on me to shift-click
Advanced Trade Skill Window – more sorting/filtering options for your tradeskill windows, plus tracks required materials in your bags, bank, and alts. Can queue up multiple items – and if an item requires subcomponents to be crafted first, it’ll queue those up, too. If you queue up a bunch of stuff that uses vendor-bought mats, you can click one single button to buy all those mats at once.
BankStatement – lets me view the contents of my bank and bank bags anywhere, on any character, on any server
CT Mod – mostly for the unit frames, but it’s got a lot of other nice features (and it’s modular!)
Deadly Boss Mods – I use it mostly for BattleGround events (visual timer on flags and such), but it’s also useful in raids and instances. Will warn you in large, friendly letters when a boss is about to use a special ability and can even announce it to raid/party for you.
TitanBar – just puts a ton of info up on a small bar across the top/bottom of my screen so I don’t have to go hunting through UI windows to find it. Things like my latency, FPS, gold, XP to level, durability status of my gear, honor gained, time, current coordinates. I can mouse over an information blurb to get more details as a tooltip.
Swindler Preventer – in an extended tooltip, will show you the Vendor Buy value for any items, if it knows (choice from 3 quest rewards you can’t use? pick the one worth the most to vendor). Also, when mousing over recipes/items found in the AH, will show you who sells it, in what zone, and for how much, if it’s a vendor-sold recipe/item – so you can decide if it’s worth paying the inflated premium on the AH or to go hunt it down yourself.
Yeah, I’m a mod freak. It’s a very memory-intensive setup, but fortunately, I built my computer out of spare Harley Davidson parts I had lying around, so it works quite well.