Sometimes, the simplest things can be the best.  The tried and true ABC Spring Plate is a great example.

Lots of folks prefer spring plates to tube devices because they just won't lock up on you.  And the spring acts sort of like a shock absorber, smoothing out both belays and rappels.  Spring plates have stood the test of time for one reason, they simply work!  With the ABC Spring Plate, you get a tough piece of hardware and a great price to boot.