So many wonderful knives to choose from.
I'd start with a mini Presidio Ultra or Mini Grip. Benchmade's axis lock knives are simply fantastic. Gotta have one of those. If you want a sleeker, more elegant model, the 707 Sequel is a jewel of a knife.
As FlaMtnBkr suggests, the Bone Collector is another excellent choice in full or mini sizes that I'd lean toward as well.
If you want something a little larger than those models, the 551 Grip is a fantastic choice and still fairly easy to EDC. Fairly inexpensive, too, for a medium sized axis lock knife.
In addition to BM axis knives, there are some great Spydercos you should seriously consider... Persistence for <$30 is an easy recommendation. Or the Sage 1 for around $80. Both are perfect for comfortable EDC. If you want to go larger, as mentioned earlier, the Manix 2 has developed quite a popular following. There are other good models as well, but those would be ones I'd lean toward.
And the third major maker whose models s/b considered is Kershaw... the Leek is extremely popular. I'd vote for a Leek or a Shallot. The Blur is a good choice as well if you want a larger size.
Sooner or later you'll probably own all of these models anyway, so where do you want to start?

Enjoy your shopping expedition... this is so much fun.