My previous company was named UsedVancouver.com, unfortunately we needed to register every city in the world, and we did, so we ended up managing about 1200 domains.... OUCH. So if you have a product that is going to scale to individual cities make sure you make it generic enough to just "subdomain" it like craigslist does.
A short and catchy domain is what you want. However it's difficult to find those, but they are out there! And more importantly it's good to find a domain search engine that gives you lots of options. Good luck!
I didn't really know what product I was building but I had those domains. It wasn't until last month were I pulled efreeme.com out and started using it... The point is get a good domain, and you'll never know when it might come up that you could use it.