I sewed my own panniers and clothing with a Swiss made Bernina Record 930. I would recommend going for a second hand machine, from the period before they were all made in Asia. Particularly if you are going to be abusing it by sewing heavy canvas or nylon.

What ever you end up with, think carefully about the thread you are going to use. I spent much time trying to get the tension right. Some machines don't take kindly to thicker thread. I used "Gutterman upholstery extra" which was a bit stronger than topstich thread, but also slightly thinner, therefore easier to sew.

Here are a few pictures: http://picasaweb.google.com/ollybike/BikeBuilding