I take it you need these for your general liability insurance? These are the 3 basics:
"Building cleaning services, janitorial" 561720 Janitorial Services
"Rubbish (i.e., nonhazardous solid waste) hauling, local" 562111 Solid Waste Collection
Lawn maintenance services 561730 Landscaping Services, Lawn mowing services 561730 Landscaping Services
If you want to "specialize" in a particular area, over and above what's here, go to http://naics.com/search.htm
and look it up by key word, then add that to the 3 basic codes. Be sure to check for required certifications or special permits and licenses for anything outside the norm.
Is the SIC for your Schedule C? BTW ~ Do you know how to build an SIC for your particular business? The NAICS site will walk you through it if you don't.