Working out at home, what do you need?

I recently started working out at home and I must say it's been awesome. I am following an intense program and am on day 17 of 90. It's hard but well worthwhile.

When I started this program I had no equipment so I had to shell out a little hard earned cash and get some fitness equipment. However it cost me less than a few months membership at the gym and now it's mine for life!

I only had to get some free weights, a mat and a chin up bar for what I am doing so far but would love a treadmill and some machines for controlled movement.