Will one power adapter work with all shipping MacBook Air and Pro as of March 2013? I have a Late-2008 Macbook White (MacBook4,1) model, and my AC Adapter broke. 

Now I want to buy replacement adapter, but since I am going to upgrade to a MBP13 or MBP15 in the next 1-2 years, I want to buy a compatible AC Adapter that works with my MB white and with my then-bought MBP15/13. The reason is simple, when I buy a new one, I'll have a spare adapter. I don't mind using a MafSafe1&lt;->MagSafe2 adapter with either the MB White or MBP.

What is the model number of a compatible AC Adaptor that I can buy? I only want original Apple products, as my adaptor that broke was a non-original and it broke after half a year. As I always buy used Macs, so I am only interested in compatibility with devices that are available (or have been available up to) today and don't know if an 85 watt adapter would work well with any Mac.
The 85W MagSafe adapter should do the trick for you.  It's compatible with the original MagSafe design and provides enough power for all of the Intel Macs up to this point.

Picking up a 45W or 60W wouldn't save any money and though they would both run all of the Intel Mac laptops they be insufficient for powering a larger (15" / 17") Mac back to life since they require 85W.

Should Apple move completely away from the MagSafe design to the slimmer MagSafe 2 design you can add the adapter.