What are the types of class E airspace?
Check out this publication from the FAA


  Class E airspace extends
  upward from either the surface or a designated altitude to the overlying or adjacent controlled airspace. When designated
  as a surface area, the airspace is configured to contain all
  instrument procedures. Also in this class are federal airways,
  airspace beginning at either 700 or 1,200 feet above ground
  level (AGL) used to transition to and from the terminal or
  en route environment, and en route domestic and offshore
  airspace areas designated below 18,000 feet MSL. Unless
  designated at a lower altitude, Class E airspace begins at
  14,500 MSL over the United States, including that airspace
  overlying the waters within 12 NM of the coast of the 48
  contiguous states and Alaska, up to but not including 18,000
  feet MSL, and the airspace above FL 600.


This image may help to visualize it 


(source)

In more general terms its the airspace that covers most of the US below 18,000ft. Its the area where a lot of the General Aviation traffic lives (although some of it is making its way into the flight levels these days)

Side note: Depending on how you look at it class E airspace is bound to an upper limit of either 400,000 feet (76mi) which is what NASA considers re-entry altitude or what The Fédération Aéronautique Internationale defines as space starting at 62 miles so either one of those can be used as an upper bound for Class E (although officially the FAA does not define an upper bound). Re-entry point is where air drag comes into play so you would be hard pressed to get a plane over that altitude. Practically speaking the jet altitude record is held by the SR-71 Blackbird at 85,069ft and the Concorde pulls in at 60,039 ft for commercial flight.