I got my SD Modules and MP3 players (which were not quite what I thought) and went looking for docs on the SD modules. But there's none posted so I emailed LC China Tech and they say they will datasheets on whatever they make.
I'd like to get opinions of the things they do make, some of the modules psych me up a bit. Like the two that look like they can do USB hosting, and the nice MP3 module and others that should take care of those "Arduino hasn't got the speed" projects.
http://www.lctech-inc.com/Hardware/
I bought the SD modules through DealExtreme, $2.60 each for 3. So far it looks like all it will take to connect to an UNO is 8 female-to-male jumper wires. If I can work them out then just about anyone should be able to use them. 
LC tells me they will beat the price on 1 or many without asking what I paid. Also they tell me they take PayPal. However their site looks like it needs help if it's to become hobby-friendly.
Of course soldering up an SD adapter is probably even cheaper.