I use a Super Everdrive V2 and it's wonderful; really easy to use. Be sure to check compatibility lists though because there are a few games with special chips that won't work. Super Mario Kart and Starfox are the standouts. This will be the case for most flash carts though (except the SD2SNES), and the compatibility is still like 95% or something.
You can get it relatively cheap from Retrogate. It's easy to just get the bare board and install it in a cart yourself if you want to save $10. Just file down a spot for the SD card. Retrogate ships from the Ukraine so it takes a while, but I didn't have any trouble with customs or anything. Highly recommended.
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shop.retrogate.com/Super ··· SED2.htmedit: and if you're wondering, there exists a good flash cart for pretty much every popular system out there, down to the
2600!