I don't use anything. I used to use chamois butt'r, but now that I am using shorts and and a saddle that really work for me (after quite a bit of trial and error), I find I don't need to, at least on rides of up to 43.5 miles, my longest this summer. To butt'r or not to butt'r is another one of many YMMV things!
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow