I think Kate Spade, although her stuff has become so trendy now. I really like her style, but now I pretty much just use my LV purses, although I also llike to use on occassion my Gucci and Burberry purses as well.
I think there are some really nice kate spade bags out there that are underrated. Since they go on sale so frequently, you can really get some deals.
I also think the Sak bags are underrated, they are so functional and cheap. I know the crochet look isn't for everyone, but the line has some fabulous and diverse options now that aren't just crochet. Even their leather bags are good quality for the price. Plus you can almost always find the Sak bags on sale for $30 or less, I think they're a good buy for a casual bag.
Nap sacks! There is nothing more comfortable for lugging huge textbooks and binders (univ. days) and nothing easier for keeping hands-free to help kids in and out of the SUV. So much better for your back, spinal alignment etc.
That said, they're not chic, and I'm not carrying one right now.. but I still love my swiss army one.