A .com can't be replaced. I would think that I would rather ahve another name rather than take another domain extension.
Unless of course you are targetted at a specific country.
there's also a .biz and .tv domain names. they would be good, but the trouble is customers might key in your url but put it as .com and the visitor would go elsewhere.
.com will always be #1. .net is second best in my opinion. .biz should only be used for businesses and .tv is good for only tv stuff. Plus .tv is so expensive to register.