HCD layouts come in very different versions:
--Self-contained layout in the middle of a room with all-around access (island)
--shoved against a wall longside or shortside (limited access);
--a section/module of a larger layout.
As already mentioned, David K. Smith has many fine HCD layouts on his website: http://whiteriverandnorthern.net/plans.htm
Byron Henderson has a nifty "Howard Terminal" HCD layout (both point to point and continuous running) on his website: http://www.layoutvision.com/gallery/id52.html
Though it requires most-around access.
If the HCD will be up against a wall, then a very different approach is needed for continuous running, usually some larger industries in the front with a few staging tracks hidden by buildings / hills in the back (figure 8's and "open top" designs which expose all the track make it look too toy train).
Also, as others have suggested, is to look at the many smaller layout designs--like for the 2'x4's or 3'x5's--and expand the design to have more scenery on the HCD.
And websites like Trainboard and Nscale.Net have HCD threads