As Troy mentioned you can pick up the box set Infinity/Escape/Frontiers which is a great jumping in point. Don't know if its is still available in the US but it is here in the UK Try:
http://www.hmv.co.uk/hmvweb/displayProductDetails.do?ctx=93;-1;-1;-1&sku=644922or
http://play.com/play247.asp?page=title&r=CD&title=171565&p=34&g=48&pa=srAlso get the live album Captured the sound of a band ready for greatness.