Personally, I can't stand it that my iPhone starts syncing every time I plug it in. I want to have it in my dock all the time and take it out when someone calls. What I don't want, is that iTunes start syncing when I put it back in the dock.

So I disabled automatic syncing on connect in iTunes and wrote this little AppleScript file to manually start a sync with one click in the dock. Actually, the AppleScript code comes from Mac OS X Hints.

tell application "iTunes"
    repeat with s in sources
        if (kind of s is iPod) then update s
    end repeat
end tell

Works like a charm! It even starts iTunes if it is not running. Export from AppleScript Editor as an application, put it in your Applications folder and in your dock.

Bonus: icon

You can even give it an icon so it looks nice on your dock. To do this, open up the application (Ctrl-click -> Show Package Contents), navigate to the /Contents/Resources folder and replace the applet.icns with a nicer icon. The following location is a wonderful gem with a gazillion icons for you to choose from.

/System/Library/CoreServices/CoreTypes.bundle/Contents/Resources

I took the Sync.icns which is a nice orange iSync icon.