CURL is good. Released under the LGPL so you can use it in commercial products without opening the entire source. Its stable and powerful. I seem to remember seeing a cocoa wrapper for it somewhere. Maybe source forge.
That looks like a pretty cool piece of code. The interface they expose is quite similar to the internal one I had for doing FTP (I was writing a tool to sync two directories). The issue I had was parsing the return of an ls command as different servers use different formats!
I remembered that the FTP stuff I wrote was from an older iteration. I ended up using some code called FTPConnection. It used to be available here and was written by Greg Hulands. iirc I fixed a couple of minor bugs I had found.
Once I get home I will post zip of that code as it worked pretty well and was small and easy to understand...
Edit: actually I won't bother. He's one of the contributors to Connection Kit and FTPConnection is in there 😀