lee, try this one, i have been referred here by several folks:
http://www.cheaperthandirt.com/ItemListing.aspx?catid=104
looks pretty good, you can also try you local law enforcement suppliers, lawmens and arrington/streicher, i have not been a huge fan of buying ammo on line, just because, well thats just me.
i suppose that it would not be a problem, and i am not a big fan of buying weapons or ammo at gun shows, unless i know the person well that i am buying from.
that cheaper than dirt looks pretty good.
your local gun shops, if you know them well are usually pretty good sources as well, a lot of them are pretty competitive with prices as well.
also one last pointer, i have found that wally world is the best place to buy, prices are excellent if they have it in stock, have not bought much .45 there, but prices on other ammo has been great.