I use a $7 Nashbar canti mounted rack and a $25 Nashbar Elite bag. I modified the mount to put the bag on the rack like an Acorn, Ostrich or Berthoud randonneur bag.
It's a big square chunk out in front of the bike. Unless you're racing, the aerodynamics aren't going to be an issue. Take a look at randonneuring gear: Big, boxy front bags mounted on low platform racks.
Here's a pic of my bike before the Flying Wheels century last summer:
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"I feel like my world was classier before I found cyclocross."
- Mandi M.