you would find end number of list if you seach google for "list of press release sites". but why would u need this. whats the purpose behind this. according to your subject , it wont help u at all to get high rank posting in press release sites.

I agree with grgmathew, I guess what you need to do is to start making an authority by building relationships rather building links. Just my opinion.

prweb.com
prnewswire.com

and other similar sites. They aren't free or cheap, but they have reach and human eyeballs actually see them. Anything else is a waste of time.

Don't even expect a link from say, prweb.com, to be worth much if anything at all. Press release sites aren't for backlinks, they're for getting the word out about what you're announcing....which then leads to backlinks.

just go to fiverr, there's a lot of providers that'll submit your press release manually to about 30-50 press release sites for on 5buck.