I just spotted this cool timer and bookmark combo by mark-my-time.com. The company suggests your child will be exposed to 1 million words if they read for just 20 minutes a day, building their vocabulary and reading fluency.
This would be a great tool to ensure your child is completing their allotted amount of reading homework. Also, you could simply assign them to a certain amount of time to read for pleasure!
Retail: US $8.95