Classic Heavy Metal vocals from the era after the initial period of scuzzier Doom are often reverbed/delayed then selectively EQed and compressed. Of course depending on the subgenre (power, thrash etc) your mileage may very - but I wouldn't necessarily go and simply overdrive all of your gear to achieve the sound, it won't sound as good.
Some engineers use the trick of saturating the vocal on the way into the desk by driving the preamp and then just applying FX and compression to the resulting recording, this adds harmonics and has a distinctly different sound. You can achieve similar results today by using a quality amp and driving it hard, or taking the raw vocal through something like a Tubescreamer, Culture Vulture or a Distressor and being judicious with its use. Don't overegg the pudding though. :-)
If you're not capable (or budgeted) for hardware, software has plenty of good offerings - the venerable Waves plugins are generally very good but very pricey; Voxengo stuff is great for the price (!) and PSP Audioware stuff is also very good quality (the Xenon limiter is awesome). If you can stretch to buying a UAD expansion card, you can get some bloody AMAZING quality software processing which is almost (even to veteran engineers) indistinguishable from the original hardware on which they're modelled.