The current F-150 offers a choice of either a base two-valve or an advanced three-valve 4.6-liter V-8, or a top-of-the-line three-valve 5.4-liter V-8. The old entry-level 4.2-liter V-6 was dropped for 2009.
By late 2010, the new standard engine for the F-150 will be a 5.0-liter, four-valve, naturally aspirated V-8, developed under the code name "coyote."
This eight-cylinder engine (described as having "huge heads") will be shared with the new Ford Mustang. Power figures are said to be approximately 400 horsepower and 400 pounds-feet of torque.
Fuel economy is expected to be comparable to the current 5.4-liter engine.
In an interesting reversal of tradition for trucks, the premium engine for the light-duty F-150 will be a V-6.
The new rear-wheel-drive version of the 3.5-liter, six-cylinder EcoBoost gasoline turbo direct-injection motor will occupy the top slot.

Ford has officially said the EcoBoost engine will arrive next year with improved fuel economy and low-end torque with a broad, diesel-like torque curve through most of its power band.
Our sources say it too will be rated at approximately 400 hp and more than 400 pounds-feet of torque. Gas mileage is expected to be at least 23 mpg on the highway.

+ 2009 Truck of The Year: Ford F-150, By TruckTrend
+ 2009 Year Truck: Ford F-150, Dodge Ram
The arrival of these new engines is said to mean the end of the line for the F-150's 4.6-liter and 5.4-liter V-8s.
The premium 6.2-liter V-8 engine (formerly known as "Boss") that will debut late this year in the 2010 Ford F-150 SVT Raptor will be limited to only niche F-150 models and the Super Duty line.
Edited Jan-20, 2009: The 5.0-liter V-8 will not be modular, as originally reported.