When the .com domain is taken or reserved, the next best option is to go for a .org top level domain. How does .org compare with .com ? Aaron says:
[tags]seo[/tags]99 times out of 100 a .com is better than a .org, but if you can get a name that costs a million for the .com and only pay a few grand for the .org version and then add $998,000 of marketing to it I think the .org comes out on top.
Using a .org can also make your business look more trustworthy if you are offering a free service and/or are a quasi non-profit. Link.