I have 2 myself: SpecTaxi.com and TaxiLuck.com, if potentially interested - pm me.
As for your name: 777taxi.com - It depends what the market is.
For any English speaking market it's not a good name. For Russian market it's better, simply because people will be saying ''Три семерки'' (''three sevens''), however even here I feel it's a bit a name from nineties for a taxi company. Also, for Russia it's best to go .ru