External Hard Drive Auto Power Off

I have a media PC which I have just an eSATA in. The 500GB drive in it is getting a bit full and I'm thinking of adding a good size 3.5" drive using an external caddy. I want this drive to power off when the computer is placed into standby (S3) and to be powered up when the computer is resumed from standby.

Does anyone know of any caddy that supports this via eSATA?

The only things I can think of so far are to use a low powered 2.5" drive and power it using USB and use eSATA for data - but then I pay more for a smaller drive. I also thought about using a smart power strip but I don't know if they work with S3 standby?

Anyone have any ideas how to achive this?

Thanks in advance.

I do know that Western Digital mybooks do this and also spin down when not in use.

Thanks for that - they look interesting. I already have a drive though so I would prefer a caddy option if anyone has any ideas?

Any eSATA caddy will do this in my experience, it's just the same as your internal disks.