Totally depends on the nature of your startup. Assuming it's a "normal" tech/software/app kind of startup, given your TC reference....
There is publicity you pay for (advertising), you earned (did something the press wanted to write about), or you generate (like building an infographic that goes viral).
Assuming you mean traditional press, the normal outlets are: TechCrunch, VentureBeat, GigaOm, Mashable, and PandoDaily. Other publications also include startup coverage, like WSJ, Forbes, Wired, Inc, FastCo, etc.
But be warned that these are press outlets. They want to cover *stories*. You don't just approach them and say "publicize me"... unless you want to pay for the ad space to do so.
If you want to buy space on those sites, check out www.buyads.com.