Ju Ju Be's are my favorite, you can purchase them on amazon less then retail and there are FSOT pages on Facebook and the Pink Room through the JJB website.
They may be a little pricy depending on what you want but hold their resale value.
there are some really nice well built diaper bags at Babies R us for under 100.00. there is absolutely no need to dump 150.00 into a diaper bag that will only be used for a year or two.
HomeGoods has really cute Jonathan Adler SkipHops for like $20-$30. SkipHops are so functional, durable, convenient...etc. Target carries them as well and I often see them on sale.