Data Services Knowledge Base

I would suggest the Congressional Quarterly, which is a subscription-based database available through most university libraries.

The link is:

http://library.cqpress.com/index.php

Choose CQ Press Voting and Elections Collections under "Databases"

Click on Export/Download on the left navigation bar

Toggle the choices you wish: [Year, Election Type, Geographic Detail].

If you want counties or districts, you can only select 10 states at a time, so it will take 6 downloads to get all states. Still, it takes less than 30 minutes per presidential election.

Another choice that is not free, but is reasonable in price, is Dave Leip's Election Atlas:

http://uselectionatlas.org/

He charges $50 per election. His results are more detailed if you are interested in all the minor political parties in an election.

Both of these choices (Leip or CQ) have restrictions on dissemination. You can use the data for research, share with your co-authors, etc., but you cannot disseminate the raw data to others.