Wow, now that's a can of worms.
But you can't answer my question unless we agree on a definition.
So, rather than attempt to make a comprehensive definition, I'll make a definition just for the sake of the present discussion:
1. Does not want to return the federal government to the functions defined in article I section 8 of the US Constitution; and, therefore promotes socialistic government programs.
2. Does not want to make abortion a felony.
3. Thinks that homosexuals should be given approval for their lifestyle in government policy relating to marriage, and in school textbooks.
4. Thinks (or acts as though) the states are simply subservient branches of the federal government.
That's a starter, if you want to add to it I'm willing to continue.
The American Conservative Union provides ratings for all legislators in the US House and US Senate on their website.
The ratings are from 0-100 with 100 being most conservative.
Here are their ratings for Senator Specter and Rep. Hoeffel: