Seems like the venerable 1N400X series has been around forever. But it gets the job done, and they are cheap. A few of the things I do need a little bit better switching speed, but that's why there's the 1N4148. The REALLY high speed stuff, I'd have to ask my friend, he's the RF and microwave engineer. Other than processor clocks, the fastest thing I have going is just a few KHz.