I looked at the official campaign web sites of the eight candidates listed at the end of this post. Each site has a tab entitled "issues." In the following google document you can see each candidates' list of issues in a way that allows for easy comparison. I have grouped the issues, by candidate, by a number of broad categories.
1. They all have issues related to the economy. Only Barack and Edwards use the term "poverty." [Note: although other sites may mention "poverty" the point I am making is that only 2 candidates thought the term was important enough to use in an issue title.]
2. Six of eight mention terms related to lowering taxes or reforming taxes (Barack and Hillary did not).
3. All had something about the environment (primarily reducing oil dependence). Two use extra terms related to environmental issues: Hillary (global warming) and McCain (stewards).
4. McCain is the only one not using the term "education" in an issue title.
5. In the area of foreign policy, only three list countries/regions other than Iraq: Edwards (Iran, Darfur, Uganda); Romney (Latin American allies); Huckabee (Cuba).
6. All list "health care" showing that this is probably the most consistent priority of all candidates.
7. Edwards is the only one who does not use the term "immigration."
8. In my "Family and values" category, McCain is the only one who does not have an entry.
9. All but Romney and Thompson have terms related to veterans' issues.
10. Three of the five republicans list "judges" as an issue term. No democrats do. Four of the republicans list the "2nd amendment."
**update** Here are some more specific comparisons: abortion, stem cell research, immigration, marriage
Web sites checked: