Here is an interesting website about conservatism:
The author defines conservatism as the following:
1. Belief in natural law
2. Belief in established institutions
3. Preference for liberty over equality
4. Suspicion of power— and of human nature
5. Belief in exceptionalism
6. Belief in the individual
As far as simple categories go, it's not a bad list; however, when defining a conservative (also known as a "classical liberal"), I prefer to use Milton Friedman's principles:
1. The scope of government must be limited.
2. Government power must be dispersed.
3. "The power to do good is also the power to harm; those who control the power today may not tomorrow; and, more important, what one man regards as good, another may regard as harm."
The author of "Conservative Resources" has another interesting post, where he compares liberals to conservatives:
It's good to see intelligent commentary about different political groups. Categories aside, I look forward to the day when America has a viable third party. A viable third party might force both Democrats and Republicans to move to the center, where most Americans are.
I wrote here that a third major party would most likely result when more conservative factions within the Republican Party decided to create a splinter group.