Oh, Ottawa, come and stop by the TravelPod office for Valentine's Day! I'd love to meet you! Heehee.
Winterlude is so awesome, check with the National Capital Commission to see which bands are playing, the shows are often a lot of fun, there is usually a LOT of dancing because everyone is so cold they're just trying to keep warm.
http://www.capcan.ca/bins/ncc_web_content_...ng=1&bhcp=1Visit the Byward Market. For dinner I would definitely recommend Vineyards. It's an awesome wine bar, underneath Coasters. They have live jazz on Sundays, Tuesdays and Wednesdays, and it's really cozy down there.
You can't miss Parliament Hill, they offer free tours daily. Go early, because usually they'll give you a ticket that won't be good for a tour until later in the day.
For museums, the National Gallery is my favourite, but I'm an art nut. For history/archaeological fans, check out the Museum of Civilization across the bridge in Gatineau.
For nightlife, definitely go to Zaphod Beeblebrox on York St. Try Helsinki or Heaven for techno music. Also, Elgin St. has lots of "typical" meat market bars and the like. If you want to go a little more underground, Babylon or Barrymore's, a little further down Bank St. They have fun shows, usually on Thursdays or weekends.
There's a great visitor's centre right across the street from Parliament Hill, if you are looking for different stuff.