I would look at:
http://www.ncdc.noaa.gov/oa/climate/online/ccd/prcpdays.html (free)
More stations (small fee):

NORMALS AND AVERAGES
Climatography of U.S. No. 20

1) Access NCDC's main web site at: http://www.ncdc.noaa.gov/oa/ncdc.html
2) Under the heading "Purchase" in the blue box on the left, select the link: "Most Popular"
3) Select the link: "Most Requested"
4) Scroll down and select the link: "2. 1971-2000 U.S. Climate Normals Products Page"
6) Select the top item: "Monthly Station Climate Summaries (CLIM20)"
7) Follow instructions to select a state and then station(s) within the state.
8) Add to shopping cart and follow instructions to order.
7) The files are available as PDF files which can be read by Adobe Acrobat (downloadable from NCDC's web page)