If you go with the CXA-1645 encoder, they are known to produce a nice stable RGB signal. That way you can get both S-Video and RGB out, if you're using it on a console. I don't really know if those chips are still available though.
Just for fun, here is a picture of the S-Video boards I made when I was modding systems a few years ago (minus the IC and a few caps). I actually used the CXA2075 (see this page for info:
http://www.videoi.com/~pietro/cxa2075/ ), so there were a few less external components on my board. Anyways, anyone who has a system I modded should be able to easily get RGB by adding the three caps and three resistors on the top left.