I seem to get into trouble sometimes with a couple of sites, because the cpu load is too high, but it is very gray to me how to determine actual load produced by one site.

Would there be a way to find out:
A. How much CPU do I get?
B. How much is my site using?

That way I can be sure to remain in compliance, and take steps to correct problems BEFORE I get a message from the Reseller telling me my site or script has been disabled.

I would be interested in purchasing an account from a reseller that could satisfy the above.

A) On a reseller you are not guaranteed anything. You are allowed an amount proportional to how many users are on the server.
B) Your reseller has to I think (it requires root access or shell, not sure)

They should be able to handle the load based on the bandwith they are giving you, unless your running processes which are eating up the memory

But I want to know how I can know my site's CPU usage. I don't want to wait until the host decides my site doesn't fit into their plan for the server. I want to be able to measure my site against a benchmark set by the host. I do not want an arbitrary decision to be made while I'm on vacation.

I think you are looking for a VPS which would allow you to view the memory usage and CPU usage of your virtual server. A reseller account will most likely not provide a way for you to find this information.

Yes, I have been booted off of two different reseller accounts. I finally moved the site over to my dedicated server, which contains many sites, and there is no change in performance.

Probably it's my own fault for signing up for sub $20 reseller programs.

It might be that your websites are using too much CPU resources but reliable web hosts usually let you know before booting anyone off their servers.