Some of you might find this ridiculous, but that's what I use.
mhcampboy
Bontakun
Interesting concept.
ArdusKane
I'm damn weak...
Simon Dean
creative
You can buy a sledgehammer + a moderately sized tyre and do sledgehammer training.It can be a form of cardio conditioning as well.The famous Russian martial artist fedor emenlianenko uses this method and he dominates in the ring(though not the only factor)