Write press releases about your site or a section of your site and submit them to press release distribution services.

Here are few sites which you may find good enough

http://www.clickpress.com
http://www.webwire.com/
http://www.emediawire.com
http://www.businesswire.com
http://www.prwebdirect.com -
http://www.theopenpress.com
http://www.free-press-release.com
http://www.pressbox.co.uk
http://www.i-newswire.com/
http://www.pr9.net
http://www.pr-inside.com
http://www.newswire.ca/
http://www.pressreleasenetwork.com
http://www.marketwire.com
http://www.urlwire.com/
http://www.prweb.com (small contribution)
http://www.prurgent.com
http://www.prleap.com -
http://www.prnewswire.com
http://www.prfree.com/
http://www.openpress.com/
http://www.softpressrelease.com