Press Release Distribution Services

I would like to begin offering press releases to my clients. Therefore I need a monthly subscription/annual membership which allows me to send out as many press releases as I can have written.

Please provide any comments on these services including how wide of a distribution and linkbacks I could expect. If you have any other similar services also please provide them.

The best options I have found so far are:
1) http://pro.clickpress.com/
2) http://www.i-newswire.com/
3) http://www.ereleases.com/

Thanks!

 

One that i found that got picked up quickly was marketwire dot com

 

Do they have a subscription plan? I didn't see one offered but I just skimmed over it.