I am very happy with my Victorinox Adventurer (Swiss Army Knife or SAK) for my daily carry. There are other models that are similar, but I like the lock feature which makes it handy for me. It is a simple knife with a minimum amount of tools on it, so it is thinner than the Trailmaster (edit-oops) mentioned above, but still is large enough for your hand to safely exert some pressure on what you are cutting if necessary.
The newish SAK Dual Pro X is an interesting knife. It is thicker than the Adventurer (more layers in SAK speak) with a regular blade, a saw blade, and a serrated blade for speciality purposes. The only thing I don't like about it other than it is thicker than I normally like to carry in my pocket is that it does not have the tooth pick or tweezers.
I used to dismiss SAK's as "boy scout knives". But for a day to day tool, they are fantastic and fairly inexpensive. If you damage a blade like I do from time to time, you can replace the knife without killing your wallet.
I also very much like the SOG Twitch II and Twitch XL models for carry. The Twitch II is small for you pocket with a clip but fast to deploy and stays sharp. The Twitch XL is a fairly new addition to my carry rotation. I always have the SAK, but often have a second blade on me.
The Mini-Griptlian is another one that I like. The new folding Razel fascinates me also and I'll probably buy one. I have the Ringed Razel which is a fixed blade and never really got used to the size and edges for daily carry. I guess I'm a glutant for pain as I'm probably going to get the folder and try it out. Who knows if I'll like it?
The Spyderco Native is an excellent daily carry knife. Walmart used to carry them and were priced in the $35-$40 area. Most of the Spyderco knives are very good. I have a couple Endura's that I use for work knives, but have been known to carry the fully serrated version clipped to a back pocket. It is the only fully serrated knife I own. I like the the size of the Delica, but have never bought one. I want to look at some of the newer ones that are similar.
The SOG Mini-Vulcan is another knife that is useful. It is a bit thicker than the Twitch knives, but is so easy to open one-handed if that is something that you like. It is also a very tough medium sized pocket knife with blade that is very sharp from the factory and easy to maintain with a diamond sharpener.