I use the basic Nashbar grocery panniers. Very similar to the Performance ones, but a few bucks cheaper. To keep from overfilling them, I shop using the store's handbasket rather than a cart. The handbasket plus a handful in the other hand (jug of milk, a couple of loaves of bread) fill them perfectly. I generally alternate between one and two-trip weeks.

A note of caution on the Cypress: When using any sort of panniers on my Cypress DX, I have heel-strike issues. To solve the problem, I use an expedition-length rack, like the Jandd Expedition, so the panniers can be mounted further towards the rear, out of the heel zone.