I think that Twitter is the best place to post updates about a startup. I've tried Killerstartups.com but the traffic from there isn't that good anymore (I think). Other sites I've found are:
<a href="http://productivewebapps.com/" rel="nofollow">http://productivewebapps.com/</a>
<a href="http://www.appvita.com/" rel="nofollow">http://www.appvita.com/</a>
<a href="http://betali.st/" rel="nofollow">http://betali.st/</a>
<a href="http://startuplocation.com" rel="nofollow">http://startuplocation.com</a>