Just thought I'd throw my $0.02 in here, because I like one direction, and the other hasn't been mentioned yet. I think the 105 RD with 32T capacity, and the SRAM 12-32 is the way to go. And as noted, you'll probably need a new chain with some extra links.

Now, there is another option but it's probably not any better. Get a Shimano M771 cassette (11-32, 11-34, 11-36...take your pick) and M771 derailleur. Even though it's a 9-speed derailleur, there is a group of guys around here that are running this and it will shift correctly with a road 10-speed shifter set (e.g. 5700/6700). Apparently works great with the 11-34 as the choice of cassette too and a compact double up front. I haven't personally tried it, but have seen it and what you're looking for sounds just like what those guys described to me when they decided to make the switch. Personally, I like the 105/SRAM combo that has been suggested by others already as the best option if you're just trying to get to a 10-speed, 32T size derailleur, but you could go a step further with this setup. Personally, I wouldn't like the 11-34 range as much because the size of each cog is getting more and more separated, which isn't great on a road bike when you're on the flats and trying to find that right cruising get combo for your cadence. So that's another positive for the 105/SRAM combo.