I peresonally prefer something that is like browsers(means no screenshots like browsershots.org) and free(not like Adobe Browser Lab).
And as IE has been the most troublesome for me testing the layout in all versions of IE is enough for me. If you want for other browsers Browsershots.org is always there for you.
My personal choice is a WebBrowser which is free and accurate. Its called IEtester and be downloaded from here.It can be used to check browser compatibility for Internet Explorer versions from 5.5 to 9.
If there are better tools or services out there for this purpose please share the knowledge here.
The choice of IETester is my personal choice and just a suggestion. I am not endorsing or denoucing any tool or services.All are great in there own way. If you have anything better in mind feel free to share here.
P.S:And by the way save water. An interesting topic about very easy methods of water conservation can be found here. Read it.