I have a pair of BushWhacker panniers, specifically the YUKON at the bottom of the page
http://www.bushwhackerbags.com/panniers.html
What I like about these is they are connected, making them very easy to carry around, just throw it over your shoulder. I commute about 8-10 miles one way and will occasionally need to carry my laptop in addition to a full change of clothes, shoes, tools, etc... @2400 cubic inches they have served me well.