Virtually everything you need to improve!

The BBC has a wonderful website for Celtic musicians. It contains fifty standard tunes, arranged in sets of two or three (by tune type) and recorded using typical session instruments: guitar, fiddle, flute, whistle, bohdran, and accordian. You can grab your instrument and play along through your computer.

They were recorded at a fairly brisk tempo, but that's the way things go at any good session anyway. The advantage is that you can repeat each tune as much as you like until you learn it. This would be tedious and unacceptable in a live session, but what a great learning opportunity on your computer! Oh, it also displays and allows you to print the sheet music for each tune. Very, very nice.