I bought this bright yellow Novara backpack from REI last year:
It was recently on sale for around $40, but I don't find it on the website anymore.
I like it. It's big enough to carry clothes, lock, pump and other assorted bicycle accessories in its 2 larger compartments and front pocket. It has a bag protector on the bottom that you can pull up over the bag in the rain. The only thing I don't like about it is the zipper on the front pocket runs vertically, and if I forget to zip it, I run the risk of losing whatever I've stashed in in it - like my keys, wallet and phone. So far I've arrived home with all my possessions and ability to get inside the house.
It shows dirt easily, but it came out of the wash just as bright yellow as the day I bought it.
But the bag is a little conspicuous, on or off the bike. OK, I guess that's the point of the bright yellow and partly why I bought it. It's noticeable. But sometimes I'd like it to scream "bike bag!" a little more quietly.
But darn REI, they're always coming out with something new and improved. So what do they do this year? They bring out the Novara Gotham backpack.
It comes in blackish or red with plenty of reflective bits. Its slightly larger at 26.5 liters. The front pocket has a horizontal opening with a flap that pulls down over it. It might be a little pricey at $99.50 but the black version wouldn't clash with my clothes - a very important consideration!
I like it, but the yellow bag doesn't need replacing yet. I know what I could do. The carry/hanging strap on my yellow bag broke last year, something I remember reading about in the reviews. I could take it back and trade it in towards the Gotham. Someone else could get a good deal on a used bag at a Scratch and Dent sale. But I just can't do that now.
I should probably rent a table at the Spokane Bike Swap March 24-25 and sell a few extra bike things I've got laying around, including the yellow bag.