I can't tell you which brand specifically is the best, what i can tell you is the cheapest way i know of to get one is ebay. Just type in Digital Scale and voila, i got mine for $20 including shipping. Just make sure it can tare down to zero, having a tray of some sort is a major plus, you want it to measure to the nearest decimal. You can get more accurate ones that go even further but alot of the time you can only put minimal weight on them. so if you only buy small bags and want it mega accurate that's all fine and dandy but any weight becomes a pain to weigh.
www.ebay.ca or www.ebay.com. usually less then $1 plus shipping and handling. Thats where I got mine. eric