i carry around a Kershaw Ken Onion "Random Task" Mdl1510ST, couldn't ask for anything better!!! I can open it with one hand in about 1/2 a second and close it with one hand in about 3 seconds.
I love it, and it is good for a variety of jobs.
They are around $100 though. Had it for about a year, no problems. Belt clip on the back too.