The first decision s whether to buy only the door or to buy a pre-hung unit. Unless you are really talented in carpentry, don't even think of installing a door yourself unless it is a pre-hung unit. The pre-hung will also be cheaper and will probably have better sealing than can be readily achieved using a site-installed door.
Materials:
Wood: Looks great, but there's no such thing as a low maintenance wood exterior door unless you have a very deep porch to keep both the rain and the sun off of it. I don't know if any wood doors are Energy Star rated--they'd have to have foam sandwiched inside to be as efficient as fiberglass or steel doors.
Fiberglass: Pricier than metal, cheaper than wood. They do look like wood. Good energy efficiency.
Steel: Energy efficiency about the same as fiberglass. They resist forcible entry well if they have beefy wood framing internally (the edges, and esp at the lockset.) Least expensive option.
Much of the choice depends on your house style--some houses don't look right with a wood or faux-wood door--in which case, a metal door is an easy choice. If I'm going to paint it anyway, I'd go with a metal door.
Are you sure you need a storm door? The new doors seal very well, and so the energy payoff from a storm door is not that great. In addition, if the sun shines on the door, the heat buildup between the door and storm door can wreak havoc on a wood door. A door with bars does make sense if you are worried about security.
The tax rebate--just because a door qualifies for the Energy Star rating does not mean it will qualify for the federal giveaway. The standards are slightly different, so be sure to read the paperwork closely.