Tool for recovering data from crashed HD

[Ow Mun Heng]

I've got a HD which seems to have problems. 
( I can't boot from it)

I would like to know what tools are available to actually
perform some kind of data recovery or something.

Currently, I'm just booting into a copy of Knoppix and then mounting
the HD and copying (what can be copied) off the drive to another network 
location.

Sometimes it works. sometimes it just hangs at scp.

Pointers??