A 7805 drawing 750mA from a 14V supply will dissipate (14 - 5) * 0.75 = 6.75W. Of course it will get hot. You need a major heat sink for that. The T0220 case can only dissipate about 1W without a heat sink.
yeah. just 750mA seemed like not a lot of power, and the things are rated for 1.5A, ...
the first one I tried using was a straight clay heatsink, but as it got a little bigger I noticed that it didn't get hot uniformly (some parts got hot, others were still cool, and generally was a pretty big mass of clay).
with the metal-dust and clay heatsink, the heatsink seems to at least get hot all over, and presumably cools better (at least, it is a bit more effective with a lot less material, but still not effective enough to work without a fan).
have noted that it seems to not get as hot when running off of a 9v back up battery (currently consisting of 6 alkaline AAs wired in series), but this was mostly intended to deal with momentary disruptions to the 12-14v source (I am using a lead-acid battery as the main battery, but power may be momentarily disrupted depending on motor activities, and the 470uF caps I have available don't seem to be sufficient to deal with this on their own, as brief losses to 5v power are enough to cause the RPi to crash or reboot).
note that input diodes are used, so that the 12v and 9v inputs are isolated.
The alternative is a DC to DC converter, which will save power and not get hot.
I had looked, most options here seemed to be either building my own, or buying something in PCB form. couldn't really seem to find anything quite as convenient as the 7805, but I may not have looked enough.