Ricci Adam’s Musictheory.net
This site provides interactive lessons and trainers that cover basic music theory concepts. Be sure to use the Key Signature Trainer, Interval Ear Trainer, and Chord Ear Trainer.
Teoria Music Theory Web
There are many interactive exercises on this website. Most topics have various ways for you to practice: construction, identification, and ear-training.
An interesting site that has resources to practice listening for harmonic progressions.
There are many interesting things to discover on this website. Theory students will find the music dictionary (under resources) to be extremely helpful in a pinch!
Web Based sequencing program
Web based program that gets the chords for any song