Here is a master list of NSF REU awards in the Mathematical Sciences: REU Sites: Mathematical Sciences. Sixty-six awards are listed.
Here is the analogous list in Computer and Information Sciences and Engineering: CISE REU sites. The CISE director tells me (7Jan11) that "The 2011 sites have not been awarded and we cannot release information until awards have been made." So the list is the current active sites that are continuing. Perhaps the same holds for the math list.