+1 on the keep the weight on the bike.
I used an osprey talon for commuting last year and it worked well, but I was only carrying 12-15 pounds.
I know it's a lot of money, but the burley travoy looks like a possibility for moving a lot weight around on your bike for a daily commute
http://www.burley.com/home/bur/page_416/travoy.html,