[rudy750]

...which services are doing it right? Got a list?

[corry]

Adobe's BrowserLab does this (https://browserlab.adobe.com/) for mainstream Mac/Windows browsers. You need an AdobeID (registration is free). I've found it much faster than browsershots.org (though you have fewer options). No mobile support, I'm hoping they add that soon.

Edit: 'no mobile support' = 'doesn't emulate mobile browsers'

[eps]

http://browsershots.org is one and they also have $ version that is allegedly better and faster.

[timxpp]

For browser-based website monitoring the best ones are AlertFox and Browsermob