We have a web application we want to start selling on a per month basis.
We have several resellers that we would like to have resell our application and make a margin on doing so.
We don't want to spend the time writing the account management, reseller sign up and all that side of things.
What sites are available where we can plugin our website into it and have the management side of the problem take care of for us?
It might be worth investigating:
http://www.avangate.com/reseller-management-software/ I haven't used it myself and I don't know how well it works for web based software/subscriptions.
It sounds like you need affiliate management. You may want to look at iDevAffiliate. We use it with our SaaS product which has a monthly pricing model.