A cost-effectiveness analysis is also important here.
$1 in the jukebox seems to be the best value if you can serenade properly.
Depending on the venue, my best results generally came from:
- I Can Love You Like That - John Michael Montgomery preferred,[1] but All4One works just fine too.
- I Swear - JMM version has an edge here
- You Look So Good in Love - George Strait has a lot of good ones, though this one's a bit specific to getting your now-otherwise-involved ex to come back for a booty call[2]
- Let's Fall to Pieces Together - George strikes again. Great if you know she's not quite to the "easy rebound" stage yet.
- Fly Me to the Moon - Sinatra just works. Gotta do it right, but it works.
- About 75% of Harry Connick Jr. songs - see Sinatra.
- Can't Help Falling in Love - Lead-pipe cinch if you can sing it like Julio Iglesias, but the Elvis version is acceptable if done well
FWIW, JMM's The Grundy County Auction Incident actually worked once, but that kind of "breaking the rules" is an advanced technique.
Of course, SCA events and renfaires don't usually have jukeboxes, so you'll need to work on songs like Red is the Rose to get your sleeping bag properly warmed on those cold nights.
[1] The bridge can be a bit tricky. The key is to be good enough to not have to do it; you can't kiss and sing at the same time, and you've got more than half the song to work on earning that opportunity.
[2] Not at her wedding, guys. That's just tacky. Serious stud points if you pull it off, but still tacky.
EDIT TO ADD: Now that's thread drift. Legit political topic -> Kim Kardashian -> Nude pics of Barbara Eden -> Economics -> Masturbation -> Serenading for fun and...well...lots more fun