I'm sure caker will hate me for suggesting this... but, I regularly under-user my bandwidth. And I always have at least a little extra disk space available.
In the meantime, I notice that a lot of small websites get slashdotted and the like by overwhelming peak demand. What I think would be cool would be to set up a fairly sturdy proxy cache system, possibly linked in with larger existing systems (like this one:
http://www.ircache.net/), and peered against each other.
Ideally, to set this up, I'd write all the tools to generate a simple squid config for those who wish to participate. And use some DNS round-robbin hacks to let people control how heavily they're donating resources (so you can, for instance, make sure you don't over-use your bandwidth, or try to use up more toward the end of your billing period).
Would anyone else be interested?