The Playtex Insulator Spill Proof cups are wonderful.  I purchase a set of two for my busy toddler of 22 months and 1 infant cup for my bubbly independent 4 year old.  It is practical are far more affordable than other brands.  The volume is perfect if you have a drinker who always wants to hydrates.

On the down side, the spill proof isn't exactly spill proof.  Once it place on its side and it drips which it's fun for me when I can't locate where the cups are.  Cleaning can also be a problem.  The valves are easy to clean but cover itself can be very tricky and the small areas are hard...