On Windows Vista or later, the whole %appdata%\Bitcoin directory can be replaced with a symbolic directory link:
(0) Make sure the bitcoin client is not running.
(1) Move the %appdata%\Bitcoin directory to its target location (e.g. d:\bitcoinData)
(2) Run the command prompt as root and issue the command mklink /d "c:\users\\appdata\roaming\bitcoin" "d:\bitcoinData"
done!
This allows you to keep bitcoin client data anywhere, e.g. on a secure local fileserver.
Guys, Really this is the better one, I literally forgot that i was using it, ive been using it all the bitcoin clients across my house's computers it works great and im even using Shortcuts instead!
Not to be the a threadomancer but this set of instructions really helped me out. Bitcoin was getting too large for my SSD and this is the perfect solution. Just make sure you backup you wallet before doing so.
Also in order to make a symbolic link we need to remove the existing bitcoin directory in the appdata folder by either cutting and pasting it or moving it all together.