I had a Blackburn Mtn rack on my Diamondback, which I used for commuting and groceries. When I got my Kona I bought another Blackburn. Mine was $13 used at Recycled Cycles.

Whatever panniers you get, be sure they have a drawstring top to keep groceries from bouncing out. Kept my groceries (an other stuff) in place pretty well.

My Nashbars had the bungee bottom-anchor attachment (below the 2 top hooks). My REIs have a weird side-ways hook thing that I don't like much. No matter how I try to adjust it, it's just not as secure as the bungee style. Haven't lost an REI pannier yet, but worry about them.