Hi Raquel, we had an event here on the forums a while back with Diana Ennen about press releases, here's an archive of that chat, she gives lots of good info that might be useful to you, including a few sites she prefers for submission of releases.

I personally use PRWeb for paid submission - they have great SEO features and releases always make it into the Google News stream, which is ideal.

Also, check the Useful Resources section of the VAF Directory for a list of release submission sites both paid and free.

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