Guam and Puerto Rico
 

These are american territories but not states. I know they do not have senators in washington but do they have congress members? Can they vote in presidential elections? And why are they both not full states?

They are behind Canada in line.:)

Because then we'd have to spend money on social services for them, which we don't want to do, and they'd have to pay taxes, which they don't want to do.

We only need to control them because they are strategic islands off our coasts, same reason China will never ever let Taiwan go.

Edit: Oh, and to answer your question, they each have a single "Resident Commissioner" who gets to hang out in the House of Representatives in Congress but does not get to vote. Basically an ambassador.

They really don't pay taxes or receive social services? I thought they did.

As far as I can tell, they don't pay taxes to the US, only to their own government. You're right, they do receive monetary aid from the US to the tune of $4.2 billion annually, much of it earmarked for public welfare costs, but their programs are mostly internal, such as "Nutrition Assistance for Puerto Rico" instead of food stamps--they are not part of the same system we are.

Well, Guam is nowhere near our coast. We picked it up from Spain as a trans-Pacific rest stop during the Spanish American war.As does DC. Though we get to vote for the President and pay Federal taxes.

Well okay, not technically near the coast, but neither is Hawaii really. It's close enough that we care about it. A lot of the other islands in the area (Northern Mariana, Micronesia, Marshall Islands, American Samoa) are also commonwealths or at least very closely associated with our government.

The bottom line, regardless of some of the other esoteric reasons, is their populations don't want to be states.

Not enough, at any rate, to pass a referendum to petition for statehood.