I was in the same exact situation. I was worried about degrading the signal through HDMI by using a switcher, and knew the only way to guarantee a pure pass through was go with an expensive unit (I find you get what you pay for in most cases). I actually found a unit that had 3 HDMI and 3 optical inputs that allowed you to switch between them, but it was like $350 or something.
I did find a $100 HDMI switch with 2 inputs. I just worried about signal purity. Probably not justified, but I am a freak about as direct a difital connection as possible. If you are more balanced, then here is the link
to this seemingly great product.
Here are two more products that meet your needs:
They are the first products on the page.linklink
But beware, I am pretty sure that not of these switchers (and maybe not as of now) are compatible with HDMI 1.3. Your PS3 is the first consumer device that will output HDMI 1.3 quality video and audio, and TV's that accept and display this better picture will be out in 2007. If your switcher doesn't support HDMI 1.3, you have broken the chain. HDMI 1.3 switchers will be out next year.
My fix was to connect my HD Cable Box via a good set of component cables and I let the PS3 enjoy the HDMI connection on my TV. I then connected both devices to my receiver via optical using an optical switcher I bough from monoprice. Works great!