The BBC's Virtual Session is very good - it shows you the written scores of popular session tunes, and also has sound files that sound like proper instruments so you can play along. Its main limitation is that it's nearly all Irish tunes. My attempt to make a blue clicky has failed, so you'll have to copy-and-paste this:

http://www.bbc.co.uk/radio2/r2music/folk/sessions/

In reply to Lynne's question, Rakes of Mallow (a reel, allegedly Irish) is related in a distant sort of way to an English tune known as Rigs of Marlow (a jig used for morris). Rigs of Mallow sounds like some sort of hybrid - they're probably all variants of the same tune, although I don't know where it originated. Both the tunes I've heard sound more English than Irish to me.

Marje