Amazon.com's buy one get one 50% off sale is back (maybe just tomorrow, could be weekend, not sure). This is the one that includes the very good DS games (Professor Layton, Pokemon, Etrian Odyssey III, Dragon Quest IX, etc.). I see a lot of XBox 360 titles that are reasonable, but not spectacular. These DS games never go on sale... ever.
When I did it last time I had Prime so I made multiple orders with 2 to each cart to get my discount to stack up properly, no idea if this is fixed.
EDIT: Forgot the link... http://www.amazon.com/gp/feature.html/ref=br_lf_m_1000647951_grlink_1?ie=UTF8&plgroup=1&docId=1000647951