Tversity: You've probably seen our PS3 streaming guide at one time or another, so you know it does work. We just wish our readers didn't have to go to so much trouble just to get streaming up and running. Still, you can't argue with free.
PS3 Media Server: A newcomer in the pack, but it also touts the highest ambitions. Using nothing but Java, PMS looks to avoid all the troubles of codec installation with a simple install-and-go package. If only it wasn't so buggy, we'd give this one a thumbs up for sure.
Windows Media Player 11: Some of you may not know this, but WMP11 has a built-in media server already installed. You just need to activate through your Tools > Options > Library > Sharing > Configure Sharing > and click "Share my Media." Of course, this means you can only stream stuff your external device supports, but it's probably the most reliable piece of software out there right now since you're not tweaking a million things on your computer.
Nero MediaHome: Pretty much the same idea as Tversity, but leaves you a few dollars less.
Twonky: Again, same thing as Tversity, except it'll run you about $40.
Are we missing any? Let us know in the comments what works for you!