Joel Morrissette

Thanks to everyone who replied. I got a broad sampling of opinions. Here's
the summary:

* Backpacks are preferrable for load distribution over courier bags.
Courier bags win where you need to get into the bag frequently. One
response warned against the risk of going over the bars during a panic stop
when wearing the weight too high. Duly noted.

* Try the pack with your helmet on. Some packs have handles that may
interfere with being in the drops or turning your head. One person
mentioned not being able to see around some packs while in the drops.

* Vaude's backpack is the resounding winner. The Siena 40 was specifically
mentioned. Many have extolled its virtues of comfort and carrying
capacity. The integrated rain fly and airflow are fine features.
Everything has been carried in this pack, from a wind trainer to somebody's
girlfriend! It's now absent from the product lineup on Vaude's website, but
it's been spotted at Next Adventure and Bike Gallery within the last year or
so.

* Pedro's makes a similar pack for a little less money. Apparently only
available online.

* Seattle Sports makes a 100% waterproof pack whose drawback appears to be
lack of pockets.

* Timbuk2 makes the Out-of-Whack backpack, which is basically the messenger
bag form factor with backpack straps.

* There are several options for waterproof pack covers if the perfect pack
doesn't come with one.

* Dieter makes a pack that sounds similar to the Vaude mentioned above.

Joel