The Monster Cup frequencies listed in flythunderbird's post are accurate. The only differences I noticed are that #31 Newman uses the 2nd freq, #95 Kahne uses the 3rd freq, and 99 Weatherman uses 453.6125 and 455.9875.
Not to sound like an advertisement, but "Speedway Scanner" offers a yearly subscription for $15. and covers all the major and many minor racing series.
Also for those who don't like to take the time or effort to manually program their scanner, Racing Electronics sells a scanner that you can program at the track with no programming fees. All you have to do is be at the track, turn the scanner on, press the "over the air" option and the scanner will download all of the frequencies including the CTCSS/DCS codes for all the series racing that weekend.
This scanner however is pretty much only good for racing as it only covers the 450.00 to 470.00 range.