I've been commuting for about five weeks now and love it. I've been using a milk crate zip tied to my rack, which has worked okay. My old rack was one of those seat post kind, which bounced around terribly when I went over bumps and sometimes even hit my fenders causing misalignment and tire rubbing.
Just today I was able to switch to a regular back rack, which I expect to be much more stable. Now that I have the new rack, I have the option of using panniers instead of the milk crate. I like the idea because I could go back to swinging my leg over the back to mount the bike. Stepping over the top tube has been somewhat awkward, but not too bad.
Here's the pannier set I'm considering, the Ortlieb Back Roller Classic: http://www.amazon.com/dp/B000NWG0MW/...I1FU6A0QPEQW05.
For a total newbie in terms of bike commuting, is there anything I'm not thinking of in making this switch? Anything that makes the milk crate a better option? Anything about panniers that changes how the bike handles? Or any problems with these particular panniers? Sorry to ask such basic questions. I've read lots of threads about panniers -- guess I'm just looking for reassurance.