To me, the obvious choice here is the newest version of the Spyderco endura. Don't be fooled by the polymer handles, which some people don't like just because of the idea of polymer handles -- the knife has steel liners for strength, great ergonomics, a great EDC or defensive blade shape, top-shelf steel, fantastic edge geometry out of the box, the hole opener, an ergonomic handle, and the price is right. Here's a link:
http://spyderco.com/catalog/details.php?product=208 If you're leaning more towards self-defense use, here is the ultimate:
http://spyderco.com/catalog/details.php?product=226 The previous attributes described, plus the addition of the wave, makes this one of the best defensive folders
at any price. Some people play down the advantages of the wave opener, but most of those people have only practiced their openings in a stress-free environment. All you have to do is some pressure-testing with a well-padded training partner, and you'll see how much difference the wave really makes to your ability to draw the knife under pressure.
Consider the waved Endura the gold standard, which is amazing because of its low cost. Any other knife beyond the Endura requires a trade-off. Again from Spyderco, the Manix and Chinook are both fantastic knives, stronger than the Endura and capable of heavier use, but also so much heavier so they are noticeably less comfortable to carry. The Stretch
http://spyderco.com/catalog/details.php?product=166 is one of the under-rated knives Spyderco has, fantastic choice for almost anything.
There are some other companies with non-liner-locking thumb hole folders, but I can't think of any that meet your specs and that I'd recommend over the ones mentioned above. The only one that I might consider is the Mini Skirmish,
http://www.knifecenter.com/kc_new/store_detail.html?s=bm635p if you're willing to deal with a recurved blade. Otherwise, it's a beauty. [edit: Oops, how can I forget Benchmade's 550. Great knife with the axis lock. While it has polymer handles like the Endura, the handles are so thick that the relatively lighter weight is offset by less carry comfort, so for me this is an easy nod to the Endura (especially with the wave option), but many people choose the Griptilian instead]