Around the time the first film came out (which I found nowhere near as bad as people were making it out to be), there was a series of cat food commercials featuring Garfield. It did not feature Bill Murray's voice, but someone else who sounded pretty good. Granted, Lorenzo Music's voice will forever be Garfield's, but since I can't imagine Murray doing a weekly animated series, whoever did those commercials would be a good choice.
Dave Coulier could prove a good choice as well. I know some people can't stand him, but personally he's always cracked me up and I think he's extremely talented when it comes to voices.