Get a trial subscription to "Fine Homebuilding" magazine. They ran an excellent article a while back on tankless water heaters with economics.
The "Green Building Advisor" website also has good information.
Either "This Old House" or "Ask This Old House" recently aired a show that featured a hybrid instant water heater. It combines a small tank with a large heat exchanger and a large burner. It's called the "Eternal Condensing Hybrid" water heater. Check them out at http://www.eternalwaterheater.com/.
I like all the Taunton magazines.
We used several Fine Homebuilding ideas when we built new in 2001.