Neil Foden has submitted a LISP routine to help automate the placement of elevation levels. Load the LISP file, then start the command by entering LEVEL at the command line. You will first be prompted to pick a datum level and value, then to select the type of level symbol you want to add to the drawing: Top or Underside. Next, pick a point in the drawing and the appropriate block is inserted and labeled based on its location from the datum. The routine loops so that you can place multiple level blocks based on the initial datum point. This routine comes with two drawings that are inserted as blocks; you must place them in the support file search path.

Update, March 2010: The author has provided an updated routine; new file attached, including required DWG files.