seriously the best diaper bag I ever got came from Avon, I think it was like $20. It had one big pouch, then two pockets on the outside for bottles.
I like it because it is small - anything bigger wouldn't fit in the basket of the stroller, and I'm not lugging it around!
I wouldn't really spend any more than that - I'm cheap.
But if you go out a lot, or leave the baby with a babysitter, then a big bag is probably handier.
We bought a Skiphop diaper bag and I'm glad I didn't spend anymore money on something more expensive. It's really not worth it IMO. Ours is a messenger type bag so DH doesn't mind carrying it around either. I've come to realize that alot of stuff I thought I wanted/needed really isn't necessary at all.
Well, you don't really say what your price range is and what styles you're looking at, but I think our Skip Hop was somewhere around $60 (it was a registry gift). The most important thing IMO is that it has enough pockets to keep things organized, it can hang on a stroller nicely (we're city people and do a lot of walking, but I think that's a plus for anyone) and that DH won't feel like an a** carrying it, because the last thing you're going to want to do is transfer contents into a "man bag" or maintain two separate bags if he goes out with the baby. I also went with black so it wouldn't look filthy.
Everyone's different, but for me, a diaper bag should be practical, sturdy and basic. I'm not the Petunia Picklebottom type, I think it's a complete waste of money and so many high-end bags are flimsy and/or too small. If you're really concerned about style, you could just skip a diaper bag and get a huge purse or shoulder bag instead.