Extra Pockets from Pickpocket tree
Merchant from Speech tree
Extra Effect from Enchanting tree
Physician and Benefactor from Alchemy tree

Also very good for just about anyone:
Eagle Eye from Archery tree (to zoom in and scout an area even if you won't use bow as your weapon, helped me a lot at lower levels)
Arcane Blacksmith from Smithing tree (unless you'll never ever use any weapon and armor piece)
Magic Resistance from Alteration tree

hahahahaha, this is a joke right? RIGHT?!

If anything, the most useful perk is extra pockets, because overencumberence is a problem everyone faces.

Thanks to everyone, all fascinating, most have pretty good reasons for wanting a specific perk (or three!). That's what makes Skyrim so immersive, for me, just as I think I have a play style / perk combination sorted, I discover someone doing something different, something I haven't yet tried, or discovered. For example, I have not explored at all the pickpocket / lockpick tree for any of my characters so far, but with the comments about thievery at night, and 'stealing the clothes right off their back', now I want to give it a try.

What's this Lycanthropy tree some have mentioned?

It's not *that* great, honestly. I've noticed a slight increase in random magic items in chests, only a few of which have been of ebony+ quality... plus you're still restricted to one enchant per item. It would be best taken at lower levels and only if you're not interested in crafting your own gear, but you still have to pick 5-6 perks to reach it, so it's definitely not amazing.

Apprentice Restoration and the perk that doubles the power of healing spells.

Even with no points in magicka, you'll be able to cast fast healing twice in a single bar. This will save your life.

From all the comments I got about that, I'm starting to think I chose it only because I svck at Lockpicking. Which is very likely.

/me visualizes the entire population of Skyrim naked and shivering, in Aggy's games....

You have no idea...

Whatever the one is which allows you to sell any item to any shopkeeper. The stupid low gold limits for everyone except blacksmiths (and theirs isn't great) means ages traipsing around selling stuff. This perk reduces the traveling - but not as much as modding vendor gold...

Let me direct your attention to:
http://www.youtube.com/watch?v=yTccvj0gc58
Just watch 1:25 - 2:15

Would it have really killed Beth to have given us a lousy 2k gold base amount on at least half the vendors in the game (all, would have been nice)? Would sure make selling off loot a lot more enjoyable and less of an unnecessary hassle.

LOL! Love that. DOOD! His PANTS?!? Whaddaya want his pants for??

I think the perk that allows the player to sell anything to any merchant. You know for convenience.