Hi Dan,
Welcome to touring or utility cycling, or both.
I want to second what others have said about quality-- panniers aren't the place to skimp. A good set will bring you much satisfaction for a long, long time. A less than good set will surely bring little annoyances before long, and is likely to bring you exasperation somewhere down the road.
There is more than one good choice, as evidence by what others say here and in other threads. For my part, I'll recommend Arkel. I've got the GT series and I love them. I've had them for well over two years, and have used them constantly and roughly through all of that time. They are entirely undiminished in their performance. The clamps, the zippers, the velcro, the frames, everything is as if it were brand new. The fabric's a little dusty, but not noticeably worn or compromised-- despite sun, snow, ice, rain, and a few gear up landings.
Whatever you buy, make sure you've got bomb proof attachment hardward, ESPECIALLY IN THE FRONT