Heres a comparison I did a couple weeks ago of the platforms of the Democrats, Greens, Libertarians and Republicans:

http://www.republicanspeak.com/positions.html

To make it a bit more interesting I used the Massachusetts Democratic and Texas Republican party platforms (rather the the more "vanilla" RNC and DNC platforms)

Disclaimer: Although all the parties positions are in their own words, I tend towards Green/Democrat so that bias may be apparent in the comparisons.

Also, there are links to the parties WebSites and platforms, so you can read the entire platform(s) if interested.