The Washington Post has this set of graphics illustrating the NRA's corrupting influence on politics. In 2011-2012 election cycle, the NRA gave almost $600,000 spread across 236 Republican candidates (an average of $2,473 per candidate) and $74,000 to 25 Democrats.
Pretty impressive numbers until you look at donations by other groups such as lawyers. I would have liked to have found donations by just trial lawyers, but these donations are still lopsided towards Democrats by a huge amount that completely dwarfs donations by the NRA. Still, I suspect that the Washington Post isn't going to run a similar spread on these numbers. Just donations to Democratic Senator Killibrand dwarfs the NRA's donations by 3.2 times.