Yes, the linear regulators do waste a lot of power in the form of heat when there is a large difference between input and output voltages. The most efficient way to get what you want is with a DC-DC converter. Unless you have a specific need for the high current (1.5A) you asked for, it's really unnecessary if you only want to make a USB charger. If memory serves correctly, the USB spec limits available current to 0.5A, so any device you plug into it won't need more than that.
There are USB car chargers available (**broken link removed**) or (**broken link removed**). There are others of course, but these are examples.
If you want to build a DC-DC converter that will supply the 1.5A, check out National Semiconductor's Simple Switcher line (http://www.national.com/analog/power/simple_switcher) of SMPS chips. A caveat here... DC-DC converters can be a bit tricky to get working. Some are very sensitive to circuit layout, and are hard to troubleshoot (unless you have proper test equipment) when they don't work.