If you are in to do it yourself projects, I just completed at 2500 mile tour with custom build panniers made out of mop buckets on a road bike (didn't have any rack mounts). The mop buckets can be bought at a place like Lowes or Home Depot for $15-20.
The first picture is just of the rear bucket. The only things you had to do it is melt the plastic a little to create a grove for where the frame mets the bike (I can't think of the technical name of those bars...) and drill a couple holes to create extre support (you can see the metel bar that I added in the first picture).
The second picture shows both the bikes (the first week and 550 miles I did with my dad, the other 2000 miles I did solo), only my bike (the blue GT) has the front bucket.
The front bucket is also a mop bucket, it required a little more tweeking.
Note: I would only recommend this to people who feel fairly comfortable messing around with stuff. Of course the buckets are so cheap, it doesn't really matter what you do with them. (I flew from Denver, CO to my home in Connecticut at the end of my trip, and I just threw out my "panniers")
I didn't have really any trouble from them, just a little tweeking here and there.