Answers

Depending on the severity of the runoff you might want to contact a Civil Engineer. As an engineer myself, with a specialty in drainage and hydrologythere are many issue to consider when dealing with offsite drainage. For instance if you redirect it on to another property it's possible you could be held liable for any impacts tha occur. Just a thought.

A landcaping contractor might help. Depending on your location, you may be able to find someone here: http://www.guildquality.com/find/Landscaping-and-hardscaping/North-America

We agree with Geoff's suggestion and would also recommend speaking with a local landscape architect. They not only handle plant specifications, but also deal with drainage and irrigation. They will be able to assist you or point you in the right direction to solve your issue.