Instead of continuing this one at a time, I'll list what I think are the main 21 differences. Some are more important than others, and some are more divisive than others.
No particular order:
abortion
gay rights
immigration
minimum wage
level of progressiveness of tax structure
corporate taxation
carbon emissions / global warming
gun control
social security
welfare
education (specific issues include vouchers, teachers unions)
globalization / outsourcing
military spending
drug law
Iraq war
war as a foreign policy instrument in general
international financial aid
homeland security and related issues of liberty
interpretation of "separation of church and state" (especially in education)
labor unions
deficit spending (Democrats being the "conservative" ones)
I'm too lazy to go into detail about my views on these issues, but as for third parties, I'd like to see a moderate (not so anarchist) libertarian party that is more willing to abandon principle (for the sake of actually getting things done) than the official Libertarian Party of America. I'd most likely vote for it, as would many others from what I can gather.