I'll put in another plug for Kirk Photo. I've bought all of my L-brackets directly from them, and since they're in northern Indiana, anything I order early in the day makes it to Indianapolis the next day.
That said, RRS is also a highly regarded brand, and you might like the quick-release system that
@mSummers mentioned. The Kirk brackets don't have anything like that that I know of, so I have to screw my Blackrapid connector into the tripod socket that Kirk provides on the bottom of the brackets. That also means that I have to unscrew it when I mount it on the tripod.