Hey Magicrabbit, you should do a search of the forums on this topic, there are several suggestions and recommendations for bags, also in the guides section, there is a huge list of bag manufacturers. To answer your question though, i recommend booq as a great company with a large selection. But do a search, you will find plenty
However, just to let you know Best Buy has pretty nice Swissgear backpack for $59 that you might want to look into. That's also the regular price on Amazon.com if you miss the sale, or can't get to a best buy.