NIH has posted their estimated funding amounts distribution since FY 2008 and projected through FY 2013 here. They have broken the funding down into 233 distinct categories, and include a distinction between ARRA and non-ARRA funding.
It is important to note that the categories are not mutually exclusive, so the same dollar may be counted in more than one category for a particular fiscal year.
This report can be useful to identify trends for a particular area of health research, at least in terms of allocation of funding by NIH. This is particularly true because of the breakout of ARRA related funding, so temporary increases in a particular area can be identified as such. With a relatively granular breakdown, it should be a helpful table of data to take a brief look at.