I needed to get a R4 for my NDS, but as it turns out the Chinese government closed down the R4 factory (or something like that), and the supply of it was pretty sparse (although they are back in stock now). Because of that, I ended up getting a EZ-Flash V w/ expansion pack for my (ahem) homebrew needs. It seems to be on par with the R4 except that fewer people use it (so less English material and more Chinese) and the microSD slot isn’t spring loaded (a pain in the ass, but not insurmountable). I think it’s a slightly better deal than the R4 because the expansion pack provides rumble, RAM (for DS Browser) and Slot-2 (for GBA games) support. Also because it was reasonably cheap and like, you know, in stock!
I bought it from DealExtreme, which has a lot of random tech components and things (I ended up buying a bunch of other useless junk). It’s kind of like the cheap stuff you can buy on Ebay except it’s from a store. It’s even shipped from HK too! When I ordered, I was worried that it would take a long time to get here (too cheap to pay an extra $13 for expedited shipping). I stuck with registered air mail, and my shipment took 12 days from order to arrival (4th), although it might have been less because there was a weekend and Labour day right before I received my order. It took 7 days (22nd to 29th) to leave HK, but once it was in Canada it was pretty quick. I broke up my order into 2 packages in order to hopefully avoid customs. One that was slightly under $20 and the other was $55. Fortunately, I didn’t get hit by customs for either packages; apparently I received a lot of LED flashlights as gifts.