How to access Windows share from an iPad?
Because there is no normally-accessible local filesystem on an iOS device, an app that "supports SMB" doesn't tell us enough. Because you can't simply copy files from a SMB share onto the iOS device.

There are plenty of apps that support SMB shares, three I can think of off the top of my head (at least as far as I recall) are: Goodreader, OPlayer, and Air Sharing.

Air Sharing is probably the most compatible for whatever you want to do, as it opens almost anything. Goodreader is primarily a document reader (txt, pdf, etc.), and OPlayer is a multi-format video player. It plays almost anything, MPEGs, AVIs, MKVs, etc.

What you want to accomplish beyond merely 'connecting to a SMB Share' will dictate the app you'll be able to use.