Basically there are two ways to mount an iMac to a table or wall, one cheap the other a little bit more expensive.
Option 1 – VESA mount plus articulated arm (approx. AUD 65 – 500)
1. get a VESA mount from Apple @ AUD 45
2. remove your iMac’s stand and attach the VESA, as shown here.
3. please note the iMac 27inch weighs approx. 13.8kg, but once the VESA mount is fitted, you can then mount it via a plate (approx. AUD 20-40) directly to a wall or get a standard articulated arm, like this one (approx. AUD 65-600).
The downside to the VESA mount is that most articulated arms are not very nice to look at to say the least, thus if aesthetics are important, use…
Option 2 – Mantis (approx. USD 800)
Unfortunately, they seem to be not available anywhere in Australia, but given the current exchange rates amazon is your friend.