This is an EMERGENCY REPAIR ONLY...any impact sufficient to bend the fork back will also put the headset cones out of true...if you don't replace the fork (and cones), you might start grinding down your headset bearings.

I've done this successfully on a few bikes with solid forks, and at least one ATB with front shocks (oil-filled dampers).

IF your forks are bent back to the point where the front wheel is rubbing the downtube on the frame, don't despair, all you need is your front axle and a couple of tools.  If they're bent back farther than that, and your front wheel is toast - and you're still around to read this - well...you're walking home, but be thankfull you can still DO that.

This assumes that the wheel isn't also bent, if it is, first repair the bend using this method here:

Find a fencepost, steel guardrail, playground B-ball hoop or whatever.  You're looking for a vertical post of some kind, preferably set in concrete, and with a diameter no greater than the distance between your fork tips.  Ideally, it should actually be @ 1/8" narrower than your fork tips.  You may use a stout tree if there is nothing else available.

Remove your front wheel.

Remove the axle from the wheel.  Use a rag or sock or whatever to preserve the bearings...you'll need them to get home!!!

Turn the bike upside down.  Place the fork tips around whatever you found (post, tree, whatever).  Bolt the axle back on the forks with the bearing cones, locknuts and lugnuts...make 'em TIGHT (but don't strip them!).

Using the handlebars/headset as a fulcrum, and the bike frame as a lever, pull down and BEND the forks forward until you can tell they're more-or-less "straight by eyeball". Work gradually, too much force all at once can crack or break something.

Note: There is considerable risk employing this method with quick-release axles, as they are hollow.  Also, if your "anchor" is much smaller in diameter than your fork width, you may want to alternate pulling against one end of the axle, then the other.  Pulling against a narrow point located in the middle of the axle can bend the axle bolt, and you don't want that.

Webmaster's addendum:

And be sure to check the frame where it meets the headtube, both before and after your repair! Any wrinkles or cracks signify frame damage. Cracked frames should only be ridden CAREFULLY for SHORT distances.

Thanks Brian!