I've had good success with both PR Web and BusinessWire.

Both gave good distribution, inlcuding being picked up by SEs.

The difference was $165 for BW and $30 for PRWeb.

If you are looking for international distribution, then I would suggest BW. Call them and have a conversation with one of their reps about what you need exactly and they can send you the appropriate rate card.

I hear PR Newswire is good too, but I can't reccommend htem since I don't use them.

Also, you should have an internal media list for your company or clients. Start building relationships with publications that target your audience. It takes some time, but it's very fruitfull in the long run. It shouldn't replace your Wire releases, simply compliment them.

Good luck.