I agree with Till, it is quite hard to find something that works well in all situations, and won't wreck your suit, but will also look good with it.
I am sure though, that there are tons of stuff out there - however, I can only recommend what I know, I would take a look at this:
http://www.tumi.com/product/index.js...FindSrc=search
You can find it on eBay (new) often for less, even on Amazon. Also, it looks really silly on the website, however, if you go into a Tumi store and check it out, you will see that it looks totally different. It looks great as a backpack, or stuff away the shoulder straps, and it looks like a wonderful mix of a tote/briefcase that would not stand out in any office setting. Also, its quite "stuffable", so you can easily fit an overnights worth of clothes in there, and then stuff away the straps and carry it in to the office.