Paul - The "Fiddler's Fake Book" and "O'Neill's" will provide you more trad tunes than you'll ever likely have a need for, but as noted above, there seem always to be local favorites not found in either of those sources.

At slight risk of thread creep, I'd be interested in hearing what folks consider to be a "slow jam". Here in the piney woods of north florida, it's generally meant to be a session intended to be "beginner friendly", in contrast to the regular sessions in which tunes are routinely played at a break-neck pace. Often a fine demonstration of virtuosity, but often also an insult to the music.