I can very much recommend Litmus for testing emails in all major (and less major) email clients. I suggest you check it out, it's fantastic.
I agree with dnordstrom, Litmus is the best online testing tool you will ever find because of its comprehensive email client list which now includes mobile devices.
Good luck with your email development, it's a tough job!
Indeed it is, it took me a few months to fully understand what you can do and can't do with an email as Outlook is a pain in the rear. Things like rowspan, (paragraph, ul, ol, div etc...) elements are all hopeless in an email as no one email client outputs it out the same way, however for example the colspan attribute works perfectly fine given you don't overwork it.