The 2009 standard mileage reimbursement rate is $0.55 per mile.
The 2009 standard mileage reimbursement rate was divided between the latter half of the year:
7/1/2008 - 12/31/2008 at $0.585 per mile
1/1/2008 - 6/30/2008 at $0.505 per mile
Different rates apply for mileage driven for relocation and medical related driving as well as for charitable contribution.
You can find the details here at the IRS web-site.
PS Please note that I'm not an accountant or tax professional, but a business person like many of you. I post this information for convenient access throughout the year. Please consult your tax adviser before making decisions based on this topic.