CROSSROADS GUITAR FESTIVAL June 26, Bridgeview, Ill. Top acts: Eric Clapton, B.B. King, Buddy Guy, Steve Winwood, John Mayer, Vince Gill Tickets: $100 2007 attendance: 28,000 crossroadsguitarfestival.com When the legendary Eric Clapton assembled a group of guitar virtuosos for an all-day show in 2004, it was billed as a once-in-a-lifetime line-up. But he organized a repeat performance in 2007 and again this summer. More than 25 guitarists will gather...