Here's a group guaranteed to get your toes tappin' and your fingers slappin'. It's a Belorussian medieval folk group, Stary Olsa. They've been around for 20 years, and have established quite the following in Europe.
Here's a studio recording of one of their songs, "Vitaut" (which Google Translate doesn't recognize, so I can't tell you what it means, but the video theme suggests it's a martial number).
Where the group shines is in live performances, where they string together several songs or instrumental numbers into a medley. Here are two such lengthy pieces.
Last, but by no means least, the group also covers many Western pop and rock tunes in medieval style. Here's their version of Deep Purple's 1970 hit "Child In Time".
You'll find many more of their performances at their YouTube channel, or on the band's Web site.