I'm a bag fiend.  I am always on the prowl for a better bag to carry my PowerBook/iPod/whatever and have a graveyard of perfectly good bags to prove it.  Then one day I happened upon bags by Spire USA.  I honestly don't recall how I found them, but I'm eternally glad that I did (as is my wife who doesn't have to listen to any more excuses for new bags laying around the house). 

At the time, I was sporting a 17" PowerBook, and finding a bag to handle my Apple-goodness wasn't easy.  Enter Spire.  Their Endo XL was built for 17" notebooks (of which, the PowerBook was the only one at the time), so I took a closer look.  The materials and build quality were superb, and it could carry my computer with plenty of room to spare for programming books, iPods, cables, and pretty much anything a self-respecting geek could need to lug around.  The icing on the cake was how comfortable it was, even when loaded down with all the crap I deem necessary on a daily basis.  Oh - and the bags even come with hard, padded, removeable sleeves for the notebooks to live in while inside the bag!

I've had the bag for a couple years, and that's a real record for me.  For one, because I haven't found something I've liked better, and two, because it hasn't worn out!  I did have one stitching issue, but under its lifetime warranty, I sent it to the [local] Boulder, CO based headquarters and had it fixed in no time at all. 

Whether you're into messenger-style bags or backpacks, they've got you covered.  So what's your favorite bag?