I use Dropbox if it's just the occasional image - very good for swapping pictures that way - but the cord is really what you need to use.
You need to stop thinking in terms of syncing, though. I know iTunes just LOVES to sync and it's the only way, but a far more user-friendly method if you know just the basics of copying, is to simply drag and drop, using your HTC Desire as a portable hard drive while connected. This is the safest and easiest way - no messing with third party software, no frustrations when something goes wrong when syncing and it's faster in speed too.
I've never heard a single good thing about syncing myself - especially not when it involves iTunes. People getting their mp3 players or phones wiped, losing access to all their songs when they buy a new computer, files refusing to sync or newer files being overwritten by older ones, etc. etc. etc.