winsunx is very reliable, but the only downside to them is they dont accept credit cards or paypal. the safest/best way to pay them is via Western Union, and they have a fee of $20.00+
but the low prices at winsunx balance that out.
another reasonably-priced, trustworthy site is
http://www.success-hk.com. i personally recommend them, as that's where i purchased my cart.
yet another site i've heard good things about:
http://www.easy-gadgets.com
as for specific carts, i reccomend:
1.) EZFlash-Advance 256mbit. this is the cart i own. it has the fastest data transfer speed out of all flash carts on the market. it supports all save types (different games have different ROM save types... other cards require the ROMs to be patched before they can work). it connects directly from your comp's USB port to the GBA linker port. Another feature is the real-time clock. I really don't see much use of this, but it's advertized as helping with pokemon-type games dealing with time. I'm not too sure though...
but best of all, the software is being constantly updated with bug fixes and new features by the creator of the cart (Borden is his name). i recommend this one personally.
2.) Flash2Advance 256mbit. another high-quality cartridge. i can't say much about this kit. it comes in a USB version and a serial version. I can't say much about this cart, except that it's usually cheaper than the EZF-Advance, and just as reliable. It also supports applications like "Pogoshell" (a windows-like shell that mimics the windows OS, allowing you to read txt documents, view jpegs, play classic NES roms. definitely a plus, but all these things can be done without pogoshell (it just makes it easier, and more organized). overall a nice card. but i've heard there are some "issues" involving the Serial version not working with the GBA-SP due to voltage issues. this can be fixed with soldering, but IMO that's more trouble than it's worth, so i stayed away from this one. also, you might be thinking "well i'd get the USB version anyway; it's faster." that's what most people think, but there have been many complaints about the USB version not being recognized by their computer. I'm sure it's a great card, but i've heard of way too many problems for me to buy it.
3.) EZFlash 2. Do not confuse this with the EZFlash-Advance. It was made by a similar team (some background info: the original EZFlash card was made by a team that included a guy named Borden. well, Borden broke from that team and developed his own card, the EZF-Advance. What was left of the original EZFlash team created the EZFlash 2.). This is the newest card in the market, and its hardware is very similar to that of the EZF-Advance. it has the real-time clock as well. I can't say much about this cart either since i dont own it, but i've read some good stuff. compatible with all save types just like the EZF-Advance. If i was in the market for a new cart, i would do a bit more research before i purchased this one (since it was released a little over a week ago), but it sounds like a good cart.
for some more info, check out these forums:
gba temp forums
