What can I say these guys rock. I just really got turned onto this band a few months back. My first introduction to them was Birth Control Live 1974. This record is unbelievable. To give you kind of an idea of their sound, it would be a cross between early Deep Purple, Humble Pie and a dash of Led Zeppelin. If you end up liking this record, definitely check out some of their studio albums. Rebirth and Operation are two really strong works. I find their early albums to be the best. The blog site Out Of Focus has lots albums to choose from. As well as many other great progressive rock bands. So, go over there and give them some love. You wont be disappointed. I can't thank them enough for helping my collection grow.
Birth Control Live 1974
Note: Bilek commented that Heavy Rock Spectacular has a cleaner Version. Thanks for the heads up.