BrowserStack looks pretty strong. Multiple resolutions, debugging tools, and, most importantly, local testing. Browser-based browser-testing is a little Incept-y, but as long as the latency isn’t too bad, it beats maintaining your own virtual machines. Only $19 for one user unlimited testing for one user, and a free trial to boot. If I wasn’t already invested in my own virtual machine setup with infinite configurability, I’d be giving this a long, hard look. Who knows, I may end up using it anyway.