It's not really about how much memory a mod uses as much as it is the CPU cycles. (Though I do prefer keeping my mods under 30-35mb if i can help it!) Fortunately, PerformanceFU will also track this for you!
Generally speaking, mods that keep huge databases are gonna kill your memory usage AND your consume a bunch of your CPU cycles while data is accessed. The biggest cuprits I see in your list:
Lootlink
Auctioneer (seriously...this is prolly like 20mb at least if you have a lot of data!)
Atlas
KTM
I'm not gonna jump on the "fanboi" bandwagon and say "ZOMG!!11! Ace mods are the best out there!" but in this case, I will definately say there are much better Ace alternatives available for these mods.
Lugwig easily replaces LootLink. There is virtually zero database on your computer as it syncs with your server to find items.
KCItems and/or Fence do a decent job with most of the basics to replace Auctioneer but it depends how you use it. IMO, some mods are just worth the huge hit to system resources and this is one of them. Just make sure you only have Auctioneer loaded on an AH alt or if you must have it on your main toon, only have it set to load when you go to the AH - then you can just /reload ui to clear it out after you've been.
Cartographer replaces Atlas and is completely superior! This mod has it all - shows undiscovered areas, coords, waypoints, mapnotes, mining/herb/treasure tracking, scaling, instance maps, instance loot, etc etc. Best part? It's all seperated into different modules so you can include only what you need and it's mostly Load on Demand so if you don't use something on a particular toon or don't care about instance maps when you're grinding mobs, it doesn't matter.
Omen/Threat1.0 really surpasses KTM in every way, shape and form. Since 2.1, a lot of people noticed how much of a beast KTM was. It uses a TON of memory cycles even when you're idle - standing around town. When you are in combat, it has so much data to parse and does so in such a way that it really bogs your system down! The only issue with using Omen in it's current state is that while you can see people who use KTM, they can't see you. :/ Until that's fixed, you prolly wont be able to convince most people to use it and if you're a tank or someone who really needs people to be able to see YOUR aggro, it's not a good idea to switch now. Personally - I'm a mage. No one really needs to see my aggro but me...so I use Omen. About half my guild already uses it and most will likely be converted when it gets to a less Beta-y phase.
That being said, if you really must stick with KTM for whatever reason, pick up
KTMCPUManager. The gentleman who's lead designer on Omen/Threat1.0 made this to basically throttle the CPU cycles on KTM when you're not in combat.
So...that's about all i have to add. heh. The above mods can all be found at
www.wowace.com/files or here on WoWI.
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*edit* I just took at look at your screenshot and wow. Ok. Drop mobinfo and pick up MobHealth3. 8mb for that? /cry Thats just so wrong!