Super card lite is prolly a good cheap option but the gba compat isn't as good as it should be and DS isn't all that great either (uses micro SD's)
Check the wiki's to find more info on compat
http://eng.supercard.cn/
http://wiki.pocketheaven.com/SuperCard
Others are M3 & G6 ( compat may be the same for M3 and G6, they are also do a lite version now and compat is very good )
http://www.m3adapter.com/
http://wiki.pocketheaven.com/M3
http://www.g6flash.com/
http://wiki.pocketheaven.com/G6
Personly I just ordered a Slot 1 flash card, the R4 from reports it seems like there are no NDS roms that won't run at all but some games are reported to have problems with single cart download play for some games
Not seen a flash cart with 100% DS compat
I will be looking for the best quality gba flash cart myself soon enough... though I did have one of the best with no gba issues, with the exception of the official nes ports not working ( cart was norm gba sized ) unfortionatly that cart is no longer available [ the card was the EZFA, not to be confused with EZF/advace II + they are not by thwe same people or even the same compat ]
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