I would use a [Web Design Contract Agreement; - this one gives you two options on intellectual property rights (depending on what you're charging your client for).
- It either gives all ownership of copyright etc to the client, based on them paying a higher fee; or leaves the copyright with you and the client has a licence to use the design in their business.
You won't find a contract template that fits your circumstances exactly, so I would add in a section for your graphics with costs for usage as you describe above.
I would suggest adding in the clause that Expat629 mentions by default. It will help publicise your business and improve your search engine rankings. If a client doesn't like it, you can always discuss it, but if you don't ask at all you won't get that chance...
You should be fine, but if you're struggling, speak to a lawyer to draft a contract to fit your situation.
Good luck,
K