My current pannier - a cheap MEC number that converts to a backpack, is just a notch too small for my commute especially on the way home when I need to add the warm clothes I used on the ride in. So I'm seeking suggestions for what to buy for a replacement. I loved the Arkel Bug, because it seemed well thought out, but it's a bit too big.

My needs:
Big enough to fit clothes and lunch, plus the occasional find from the lunchtime farmers markets. But not so big that everything gets lost
Space for a U-lock
Side pockets, or a separate front pocket for me keys and the pass I need to get into the bike room
A shoulder strap, or comfortable handle for taking it up to the office
Somewhere to clip a light

Oh yes, and I'm in Canada, so that rules out REI and Nashbar and all those guys because it's too much hassle to pay the shipping and fret about the duties.