Numerous ones including the US Airways Alegheny, PSA, Arizona Cardinals, and HP Retro Jets. Speaking of HP, back in their day I flew their Teamwork Coast to Coast and Arizona 757s. Also the AS 737-900 Retrojet.
My favorite special livery I flew on was this one:
http://www.airliners.net/photo/Briti...436/1043837/L/
These were all signatures supporting the London 2012 Olympic Bid...which it won. I like to think the plane helped