I second this. I just got a PS3 and this software has worked fantastic so far.
The newest version is called Universal Media Server 2.1.1, since now the software not only works with PS3, but with XBox and some other devices as well.
Serviio is another option that I have used to stream to devices in the past, and it worked okay, but I would put what I mentioned above a notch above it.
You may want to considered a wired connection to your PS3. Wireless connections are great things, but nothing beats an old fashioned cat 5/cat 6 cable run to your router, in terms of speed and reliability.