The Supercard SD is going to stick out, as its a bit larger than a standard GBA cart.

I would recommend something a bit more recent, like the EZF4.
http://www.dealextreme.com/details.dx/sku.11179

 

The G6 Lite uses on-board memory so you can't expand it. For that, you'd probably want a device that uses external memory.

Of course (and I failed to notice this earlier) the G6 Lite is useless to you since it fits only in DS Lites, not Phats. For this reason alone you should look into a replacement.

If you're mostly interested in DS gaming, why not consider a slot-1 device? They're much easier to use for DS games and homebrew. MicroSD cards are cheap enough that you can pick up a cheap 1-2 GB one for less than $20, which is really not that bad of an investment.

 

There are several that do, including the Supercard SD.

 

Thought that was only for the M3 Lite, not G6 Lite too. My bad.

 

It still seems rather silly to base your entire purchase on the type of media you currently have. It's a factor I'll admit, but personally I'd look into the form factor of the product first and make the decision on that rather than attempting to save $20 on media cards.

I have a camera that takes SD cards, but I'm so happy I got a Supercard miniSD instead of SD since it now fits flush in the DS Phat, plus I can insert/remove the miniSD card without taking the Supercard out of the DS. This is a LOT more useful than it sounds at first, and if you got the Supercard SD you'd have to take it out before you could remove the SD card from the side of the product.

I'd still suggest a slot-1 card though. The Supercard team does continue to support the slot-2 Supercard line, which is admirable, but it's unknown for how long this will continue. You'd also get more features and the ability to use clean DS roms on a slot-1 device. Slot-1 devices work on their own without needing a NoPass device to boot them into DS mode (I didn't notice you say if you bought a NoPass or not - without one, you'll be limited to GBA mode only). In addition, there's a good chance that the DS's successor will get rid of the GBA slot, something you may also wish to consider.

Slot-2 Supercards are still great for DS gaming, but unless you are really interested in DSLinux or certain really old homebrew apps prior to the advent of DLDI, you should consider a slot-1 device instead, possibly adding the cheap $20 EZ-V 3in1 expansion pack to give you all the other benefits of a slot-2 device (GBA gaming, slot-2 RAM, rumble).

 

Ah, then in that case you would probably want a slot-2 device after all. It all depends on what you're using the cart for you see. Though I'll still recommend the Supercard miniSD rather than SD, especially if you're going to be doing a lot of card-swapping for testing applications. It's your call though.

I'm highly interested in seeing what you can port to DSLinux, so I wish you good luck with that.