Some people find it useful to punch into google "mycategory + submit URL".
You usually get all the on topic pages that offer a link submission to their site...even without reciprocating. Good way to get off the ground.
Otherwise I create a template e-mail to cut/paste/send to people, depending on how their site is laid out and how they request submissions. The trick here is, IMO, not to sound like an automated e-mail...ie insert-company-name here etc.
Otherwise you might want to look at DMOZ and all categories relevant to yours and work your way down the lists. Worth a shot.