Couple questions about the night life in Concord:
1) What are some of the better bars? Any good pubs?
2) Are there any nice/fancy bars with (preferably) live jazz?
Yup, that is pretty much the only game in town. In nearby Acton, Rapscallion brewpub sometimes has live music (check the Events page on the website). Battle Road Brewery and the Pleasant Cafe, both in nearby Maynard, have live music at night, especially on weekends (check the websites)..
There is a nice bar at Chang Ann's. Doris Kearns Goodwin hangs out there.
Chang An has great Mai tais! We tasted them all over Hawaii and could not find a better one.
Main Street Market & Café has music many nights.