Billy Gibbons of ZZ Top can be described as having a blues influenced style that frequently uses Pentatonic scales, but always with a swagger and boogie that became known as the signature ZZ Top sound.
Key playing points;
Blues and Pentatonic scales with rhythmic syncopation
melodic solos with frequent use of double stop licks
mastery of creating drama and intensity with just a few notes!
Billy Gibbons player study - Interactive TAB
Billy Gibbons on 'Guitar Moves'
Here's a video from the excellent YouTube series 'Guitar Moves' where the man himself talks about his influences and techniques! Billy plays without a pick here, which isn't my forte - but is certainly something to attempt if you want to really nail his style.
Here's a coupe of great videos on the top gear to use to sound like Billy Gibbons, both BY busting the bank and WITHOUT busting the bank.
But remember - tone come from the fingers more than it does the gear! Don't believe me? Re-watch the Guitar Moves video where Billy uses a Fender Telecaster through a fender amp, but still sounds like Billy Gibbons! ;)