I'm wanting to travel from the U.S to Thailand for two weeks, then to Cambodia for two weeks, and back to Thailand for two months. Will a single entry tourist visa allow me to do this, if not what are my options? 

I think it will work, just about. You will need a re-entry permit to keep the entry on your tourist visa valid for your return, and an extension of stay for the last month of your stay. It works like this:

• Day 1 : Arrive in Thailand and receive a permission to stay until day 60
• Day 15:  Get a re-entry permit for 1,000 baht (this can be done earlier) and depart for Cambodia
• Day 29: Re-enter Thailand and be stamped back in until day 60
• On or about Day 55: Visit immigration office and get a 30-day extension of your 60-day stay (allowing you to stay until day 90)
• Day 88 to 90 (approx): Depart Thailand

Note that this allows a maximum of 89 days from first entry into Thailand until your departure to return to the US. This will generally be slightly less than 3 months, but you are asking for 2 months plus 28 days, generally OK.