I like using Trello, but my company might block the site at any time so I am uncomfortable really depending on it. Is there anyway to buy a version to host within my company?
No, currently there is no ability to do that and there are no plans to provide something like this either.
Quote from the Common Questions post on the Trello blog:
Can I install this on my own server?
No. I can say with a lot of certainty that we don’t plan on doing this. We believe that the majority of people are becoming more comfortable hosting their services and the boost in dev productivity we get by only having one platform to test on is immense.
There is an open source clone of Trello, that is actually quite good! It's called Kanban, and it is shockingly similar feel to Trello
Very cool. It only has the basic features at the moment (attachments, calendar, tagging, etc aren't there) but it does boards comments and cards very well, and that might be all you need.
It's also noticibly faster than Trello, and you can put it in your LAN
Yes you can, check out
which is like trello is derived from