I'm not as up on this as I used to be but I can throw out some info.
It depends on exactly what you mean by mathematics. On the most applied end are the statisical geneticists and on the most theoretical end is mathematical biology. + about a trillion things in between including stuff like biomedical optics and image processing.
Statistical Genetics: Theres the big 3, from east to west: Broad Institute of MIT and Harvard (Eric Lander and team), University of Michigan (see Mike Mike Boehnke and Goncalo abecasis + the Thousand Genomes project) and University of Washington (Debbie Nickerson + colleagues). See also Russ Altman at Stanford, Kenneth Lange at ucla, Neil Risch at ucsf, Aravinda Chakravarti at hopkins,
Mathematical Biology: The Arizona State program is killer. Trachette Jackson at Michigan. University of Washington has some great people. I love the arrythmia modeling work at hopkins and ucla (see James Weiss and Alan Garfinkel... do not confuse this James Weiss with Bob Weiss the inflammatory guy from Iowa.) and michigan just invested in a huge arrythmia modeling group.
Biomedical Optics: U of Rochester + Wellman Center of Photomedicine
Network theory (genes, gene-rna, gene-RNA-protein, etc): LOTS of people here and I'm not up enough to go through them. One stand out is Eric Schadt who actually worked for Merck (yes, the drug company!), then rosetta, then Pacific biosciences.
Bioinformatics: Vanderbilt for sure. Isaac Kohane in boston. Could bulk this up more but those are the first that pop to mind.
.... lets see what else is there...
I have no idea about image processing. Aside from the Laser stuff, I find it deadly boring and dont read it. And OH MAN, systems biology. There is just no way to even summarize all that stuff. I'll leave that to the next poster. 🙂
That it for a quick review. I'm SURE that I've left out a TON. No one get offended. I'm years out of the game AND post-call ... but those are on the top of my head.