Ralph,
I recommend that you match the drill motor to the length of the
auger. Most 1/2-inch CORDED drills, such as a Milwaukee, DeWalt,
Bosch, etc. available in home centers should be able to handle a 7-8"
auger and give decent performance.
Once the length extends from 17" and up, it is advisable to
consider a drill motor such as the Milwaukee Hole Hawg, Milwaukee
Super Hawg, DeWalt DW124K and the Makita DA4031. Lesser drills are
prone to bog down at full penetration and may not be able to back out
the auger. These units are available for rent at reasonable daily
prices if $200-$350 purchase price is a bit steep to own one.
Tom

Ralph D asks:

I am looking for some advice on what companies have the best
reputation for ship auger bits that can be used with a portable drill
with a 1/2-inch shank. Any suggestions on specific models and how to
order would be most appreciated.

I am looking for a 1/2-in dia bit that is in the 18-36 inch length
range. I would like to keep it under $50, but would consider up to
$100 for drastically superior performance.