I still have an original R4, it works no problems! But definitely avoid all these R4 knock offs, like Cress said... They will most certainly wreak havoc upon your DS or DSi, rendering it to a worthless paperweight!
I have read lots of reviews, and it seems the AK2 or the AK2i are the best on the market ATM.
If anyone is still looking for a place to purchase a homebrew card here are some recommendations. I have purchased from
http://www.realhotstuff.com/ 6 times, for homebrew cards, all with no problems and with pretty quick shipping.
You could also try
http://www.ishopvideogame.com/
gbatemp also has reviews on all of the hardware, they are worth reading:
http://gbatemp.net/index.php?dynamic=8#slot1