For mine I just asked on the relevant subreddits to come check it out and give feedback. Got my first 100 users that way. + they helped me design the site:
http://styleguidance.comAs far as bloggers, unless you invented Google(or worked there) or have millions in funding, it's probably not worth bothering since you won't get much coverage(from the bigger sites). And the type you'll get will most likely get you a few hundred visitors. i.e. a 50,000/mo blog, sent me 5 people.
And the traffic you get from doing a "launch" is usually garbage anyways. And will evaporate within a few days. Unless of course your core users are entrepeneurs who read tech blogs. Then you might have some luck.
Basically a launch doesn't really get you anywhere, you should see "launch" days, as a way for you to declare for yourself that you are open for business. So that you can get serious about marketing.
i.e. for my launch date, we got 5 stories, and a total of 668 visits. That was November 18th, and last month we had 35K visits, Page Rank 5, Sub 100K Alexa Rank, Sub 20K U.S. Alexa Rank, 2K questions(content), 1550 twitter followers, 960 Facebook Fans.
So don't worry about planning for a spectacular launch, just do it, and then get to work.