I recommend you to buy an AceKard 2 if you want a very good low budget card with many features through custom firmwares and support of sdhc cards up to 32gb or an AceKard RPG, it can run the custom firmware AKAIO as well and it has a built in NAND memory of 1gbyte and a sd slot for microSDHC cards up to 32gb. The NAND flash can be acessed through a mini USB cable and the micro SD thorugh a micro sd reader. It is good that the firmware of the AceKards is openSource, because if years later the AceKard Team is dead someone can still develop a custom firmware for this wonderful card. I have both of those for 1 and a half years now and they are working perfect, the gui is a little bit windows-like, with the start button and windows, you can change skins that you can find on skin.acekard.com and in the gbatemp.net downloads, you can cheat and play gba games with an ez flash 3in1 that is plugged in in your slot 2 of ds lite. ANother cool thing is, when you have an AceKard RPG you can copy files between the NAND flash and the microSD card, in this way you can copy a game for you friend that has a flashcard in seconds, both cards also support ds download play really good and homebrew is running perfect.
Another card would be a Supercard DS one, I don't have one of them, I only have a Slot2 supercard, but from what i've heard the gui is really slow. Then there is also a M3 real that comes with a rumble ram pack and a gba pack in the package as deluxe edition and you can make m3 skaura on it. I don't know more about this card because I don't own it. I wouldn't recommend to get any R4 fake or sth else because they are really bad clones and some of them can simply break your DS