Must have AddOns?
Blizzard_AuctionUI
Edit: Oh, yea, the serious part...
Well, some input on your suggestions:
Cartographer? No way, this baby eats way too much memory and has lots of features the average user doesn't even need. If you want to scale your map and have everything discovered and some coordinates added, get

.
Bartender3? Get

. But I guess you don't even need any action bar AddOns at all, default works fine for many people.
Auctioneer? Guess we can discuss that several hours actually. I myself think that Auctioneer is completely useless. Almost nobody is using the auction house to make lots of money efficiently. You can make some money off the auction house if you really need it without Auctioneer. This eats 3.5mb average, which is a bit too much. The only feature I like about it is saving the price you put an item into the auction house in with.

does that for me
Mobinfo2? I must admit, it rocks. But this one also eats quite a bit of memory, and it's outdated a bit already. And almost nobody needs that much information on mobs previously killed. If you need a mob's health, use

. (Note: If you want to use this with the default unit frames, you have to use

)
Titan Panel? FuBar is more efficient and has cooler PlugIns. Enough said ;P I won't link that though, only FuBar would be rather useless. Visit

if you want to get it, lots of PlugIns on there too.
Quartz? Ok, I must admit, I'm using Quartz myself, and it rocks, but still, for the average user it's a bit too much. I suggest

.
That's my criticism on your choices. I myself have to say, there are not "real" must have AddOns, it's not hard to live without any actually