URLWire
URLWire, run by linking expert Eric Ward, can be a good option if you want a specialist promoter to act on your behalf to attract the interest of website reviewers.
As an example, the Dr. Mani Children's Heart Foundation used URLWire right before Valentines' Day to raise awareness of Congenital Heart Defects so that these life-threatening defects get recognized and treated before it’s too late: http://urlwire.com/news/021307b.HTML
URLWire offers two service levels: basic and advanced (http://urlwire.com/payment.HTML). At $695, the "Advanced Site Announcement" option includes basic postings plus distribution of your announcement to 300-400 journalists and bloggers that report on websites like yours.
On the other hand, for about the same cost, you could use a traditional newswire service, such as PRNewswire or BusinessWire, to announce your website to a less targeted, but national audience of reporters.