Ok, my 2 daughters have a DS each, they got them last xmas, i bought them a card each, but i tried 2 different places. 2 different cards. 1 of the cards was faulty, thankfully it was the 1 i bought from Liverpool so i took it back and they exchanged it, sadly i cant recall what card it was, but they didnt have anymore of them, so they gave me a different 1. Its called a EZFLASH V, my other daughter has got a TTDS/DSTT card, like the 1 i gave you the link for.
Both have 2GB memory cards and i havent had problems with either of the current cards. My son is getting a DS this year, so i ordered him a TTDS/DSTT card and a 2gb memory card. I have heard that there are a number of cards on the market that are infact fake, they dont work at all. Thankfully i have never came across 1 of these, i have tried my sons new 1 and that seems to work fine.
So i would suggest you get this card :
DealExtreme: $13.90 TopToy DSTT Card for NDS Lite + Sandisk 2GB TF
I dont think you can get 1 cheaper with a memory card and ive used it for the last year and no problems. It comes from Hong Kong, so it usually takes about 10 days to come, maybe longer this time of year and it would be a complete bitch if it was faulty, but from reading the comments people have left they will exchange no problems, its just the pain in the arse shipping it back and so forth.
This 1 is cheaper, but it says on back order, so you will wait even longer :
DealExtreme: $11.99 TopToy DSTT Card for NDS Lite + OEM 2GB TF
The prices are US Dollars, but somebody, im not sure if its paypal or these robbing bastards charges £1.50 for paying by debit card, so add that on.