The IRS has just announced mileage rates for 2008:
Business: 50.5 cents per mile, up from 48.5 cents in 2007
Medical and moving: 19 cents per mile, from 20 cents a mile in 2007
Charities: 14 cents per mile, no change from 2007 as rate is set by Congress
See http://www.irs.gov/newsroom/article/0,,id=176030,00.html for the official IRS notice.