Do you want a client or a server? DSFTP acts as a server, so you can use an FTP client on your PC to transfer files back and forth. Also search for "lilou" as he's just released an FTP tool of sorts that I haven't really looked into that much.
Lilou FTP is a server and a client. It's also an HTTP client. I haven't used it myself but I've heard cases where this program and the ones mentioned above can sometime corrupt your memory card forcing you to reformat it.
Why exactly would an FTP server be bad? It would work, right? I transfer files to and from my DS using DSFTP all the time. If not, try Lilou FTP like has already been stated and run the FTP server on your computer.
i know not for me mainly cause my friend is an idiot. Would be so easy for him to connect to wifi where ever he is (none at home) and grab them from my server, other then him tring to setup a server where he goes and me sending to him