A great addition to OmniRemote is ORDesktop available at ORDesktop.com.
It allows you to input Pronto hex codes, easily available on this site, and then download them to OmniRemote in your PDA. You shouldn't find too many codes that you won't be able to find in the Pronto area.
It also allows you to set up all of your pages on the PC, which is quite cool.