I RSS Submit with 4 tools, some duplicate sites overlap. Here's what I think about the tools I use (many mentioned already) - 2 of them can be found cracked.
Scrapebox has a RSS Tool that works pretty well. About 100 sites.
I also use RSSbot from Incansoft. - I hate their GUI's, works for about 35-40 sties. (Can be found cracked)
RSS Submit is also a bonus. Number of sites depends on if I feel like manually filling out some of the forms. (can be found cracked)
SENuke - 20+ sites, easy, 'nuff said.
You should own scrapebox anyways - it's only $57 and does a ton of good stuff - between that and the two tools you can find cracked you will have a complete RSS submission package.