stores:
amazon.com to get MicroSDHC cards
Very good prices on flash memory
8GB MicroSDHC Card
you should get an 8GB instead of 6GB if you plan on adding a lot of videos
if you have 26 episodes that run 24 minutes long and you encode them at a high-ish quality they will come out to ~1.2GB in total
Movies may turn out about ~250MB
dealextreme.com to get cases and etc.
low prices, free but slow shipping
you can get:
nice retractable styluses
Skins (Currently Sold out)
Crystal Case
pouche
Screen Protector
(If you want to save some money on the flashcarts you can get and "EDGE" card, it is a clone of the CycloDS Evo and its only ~$33-$43 but it is hard to find)
and other things
I also recomend that you get an
EZ Flash 3-in-1 Expansion pak so they can play GBA games
(GBA games require extra RAM to play, so they can't be used with a slot-1 card alone)
where you can buy flashcarts:
dealextreme
free shipping (slow)
low prices
most cards go out of stock fast
electrobee
Shipping is not free
prices are a tad high
limited selection
kickgaming
prices are ok
stock is ok
gameyeeeah
good stock
fast, cheap shipping
ok variety
consolesource
good stock
good variety
amazon.com
mostly sells clones
jandaman
pretty good prices
ok stock
gameyeeeah if you want good shipping and pretty good prices
dealextreme if you want low prices and shipping is not important
you can look at
this thread on gbatemp.net to see more
skins take up very, very little space. about 1MB at the most for a skin
most flashcarts can do what you want to do, if it has homebrew support it can most likely run it.
HomeBrew to get:
MoonShell - videos, music, eBooks/text, pictures (requires videos to be converted to .DPG)
DSOrganize - music, eBooks/text, pictures
Emulation:
lameboy - GB GBC
SnesDS - Snes (number of working games is very limited)
SnemulDS - Snes (Slightly better than SnesDS)
jEnesis - Genesis (plays many games + sound support)
GBA ExpLoader (this is really a loader, you need a slot-2 expansion to use it)
you can look around Urza's top homebrew thread
Here to get some ideas (its from January so some things have been updated)
There is much more, you can browse the gbatemp.net homebrew section of the download section
Here
as for games only a few of them are any good
this took a while to make, hope its useful
if you want to make an (animated) Gif you'll need to find a program that can do so, just search google for "gif animator"