Besides room bump-outs, the book even covers the option of adding on with modular housing units, pictured above. Pre-fabricated modules (similar to those units you often see acting as offices on construction work sites) are lifted into place by crane and tied into the rest of the house.
Will you add a modular unit to your house? I suspect that 98% of homeowners will choose a stick-built addition (built on site from lumber), but it's always good to know what's out there.
Black & Decker The Complete Guide to Room Additions even goes farther afield to show you options short of an addition: basement remodeling, attic conversions, and garage conversions. In a sense, these non-additions might serve to talk you out of the expensive room addition.
Should you go one of those other routes--well, they've got a guide just for that, too. See our review of Black and Decker The Complete Guide to Finishing Basements