Spyderco Endura. I lost my first one in a snow bank at a bus stop years ago. When the snow finally melted, I went out and found it. It had been buried in salty snow for 2 weeks with city buses running over it, and when I got it home, all I had to do was buff a light coating of rust off of the blade with a Brillo pad. It cleaned up like new.
I still have that one, and keep it in my car. I have a new one I carry every day. Crazy sharp, and the thumb-hole opening is awesome.
I carried a Spyderco Endura as well for years. I switched about two years ago to the Tasman Salt but still have my Endura at home and use it all the time. Hard to beat a Spyderco.
Here some options I choose from to accompany me on a daily basis: a CRKT Polkowski Kasper fixed blade, a CRKT Elishewitz Pharaoh auto (2), an S&W HRT, a Buck assisted opening, a Kershaw assisted opening, an S&W mini Magnum auto, a Puma mini, and an S&W Border Guard. Except for my custom Pharaohs, most cost less than $25, but serve me very well.
My current everyday carry is a Smith & Wesson Extreme Ops Rescue knife. It also includes a seatbelt cutter, and a window punch. Many people may find those features hokey, but I am a big advocate of maximizing capabilities. The knife is used primarily for utility purposes rather than defensive tactics. However, I am currently in the market for a good defensive blade.
I have to be honest, my all time favorite knife is still a Stilleto switchblade with a 4 3/4" blade. It's light, concealable, easy to handle, easy to deploy and has an intimidation factor that not many other knifes can match.
Order now and get a second knife free! Just pay shipping and handling.
Anyway, I love the SOG Flash II. I like 'em because they lock closed and the way the clip is designed, when clipped to the edge of my pocket, you just see a bit of the clip - none of the knife shows. You can get aluminum, black, camo, etc... on the handle and the knife, and you can get all straight blade or half straight/half serrated. I also have the Flash II Rescue version, which has a curved tip, so you can slide it along something to cut a strap without cutting someone.
I used to Carry a Boker AK-74 auto, but I lost that into some dark abyss last year.
I wanted another auto-opener, but I became a fan of Cold Steel knives and they don't make any auto's. I now carry a Cold Steel Recon 1, it's a big mama-jamma folder (9.5 inches open). If you open the blade and put it in a vice, you can hang 300 pounds off the end of the handle with no breakage... Mine is partially serrated, not shown in the photo.
It's a nice flat and lightweight rescue knife with tanto-blade and glass-breaker in the end. It also has a belt-cutter built in.
I've chosen this knife because it was hard to find a good knife that is allowed to carry around in Germany. We had some changes in the local "weapons law" that disallow a lot of knives.
Eickhorn is a German company known for some military knives like the "Kampfmesser 2000" or the LL80 paratrooper knife.
Emerson Roadhouse (in the middle. Other two favorites are Benchmade AFCK on top and Benchmade CQC7 on bottom - both discontinued - shown for size comparison.