I second the musictheory.net as well as the Practica Musica (I used this when I taught 8th grade band). Is Practica Musica still around?
Just wanted to add some tunes that helped me with intervals:
m2: Dvorak 9th, Mvmt 4 intro
m3: "Impossible Dream" (
Man of La Mancha)
M3: "O Mio Babbino Caro" (
Gianni Schicchi)
M6: My
Bonnie Lies over the ocean (as opposed to "body" -- that's a little too Al Capone-ish..

)
m7: "Somewhere" (
West Side Story)
M7: "Bali Hai" (
South Pacific)
Have fun in Music Theory! It can be a bear, but it's definitely a necessity!
Liz