This website has practice exercises for everything from note dictation and clef reading to harmonic progressions and the construction and identification of seventh chords. The "exercise" page, which this link goes directly to, houses all of the practice resources.
This website lists intervals and shows them on the treble clef. There are also tabs on the side to notation, rhythm, meter, tempo, musical form, scales, chords, and harmony.
Learn the names of the lines and spaces of the bass clef with this interactive online game for free.
Saw one for treble and figured we could use a bass clef as well!