Below are some ideas / reference material for soloing over a C dominant 7 chord. Wherever "pentatonic" is indicated, I am refering to a "minor pentatonic".

C Mixolydian mode (F major scale)
Em7b5 arpeggio
A minor pentatonic (C major pentatonic)
C Lydian b7 (G melodic minor scale) - #11
G minMaj9
Gbm7b5 arpeggio - b5 sound

Triad Superimposition

Bb and C major triads