Just picked up a new set of rules from Two Hour Wargames called Star Navy 5150:
http://www.twohourwargames.com/5150starnavy.htmlI've not gotten through the entire thing just yet, but so far it seems like a really solid rule set! It has pretty much everything you might want, including ship construction rules and a campaign system. I'll do a more detailed write-up once I've read a bit more.