See FAQ #7 in the below:

http://www.microsoft.com/express/support/faq/

"Can I use Express Editions for commercial use?
Yes, there are no licensing restrictions for applications built using Visual Studio Express Editions."



Personally, I use the Professional edition. But I don't have to pay for it personally :-)

If the free product does what you need, stick with that. The Standard editions are a pretty good deal, however. It's a great IDE IMO.