There are tons of good ones. PRnewswire maybe? I think for SEO you need more than just 1 press release submission, you need lots across multiple sites.
Press Releases are not that good for SEO anymore. Google has discounted those links because people were abusing the method. Most PR are not really Newsworthy. They are great still to get something "Newsworthy" syndicated. Really doesn't matter because they get syndicated to thousands of sites. There are free sites that provide this service too. I've just released a PR of my own today. It gets picked up by Google News also.
PRWEB and Marketersmedia are the best press release sites for PR submission. Both are the paid sites but helps to increase the traffic for your site.
www.prweb.com is the best, but make sure you do not over-do in any elements of off-page SEO these days
yes, prweb and prlog.org is one of the good website of press release. Prweb is paid press release and prlog is free and paid as well.