Is the stem dying?
 

One of my orchid's blooms are falling off. They all fell off at the top, adn now the very top end of the stem is starting to look skinnier than the rest of it and it's turning a light brown and looking shriveled.

It's changing color right where my finger is. It's supposed to be green.. Does that mean it's not getting enough water or does teh stem do this after the blooms fall off?

It appears that the blooms that are still there are on little side branches, right? I am going with this is normal and the stem is dying back after blooming.

Should I cut the stem off where it's brown or just leave it? I don't want the plant to waste energy on a dying part of the stem. What do you think?

If it's brown, cut it down. If it's green, don't be mean. :) I would trim the brown part back, carefully.

The flowers are now slowly withering. The plant has given its energy to these flowers and that is it. The moisture is the only one sustaining it.
When all of the flowers are gone, cut the spike to one inch from the bottom to signal to the plant that it needs to grow new leaf and new roots to gather enough energy for a new spike on the next bloom cycle.

Agree with everyone! Bloom show over, it will rest for awhile, then resume growing new leaves or roots, for next season again. If it has never been repotted, it will be a good time to check on the roots, do some trimming, new media.

Agreed, cut of the dead part, but don't worry it's just normal for the flowers to drop and for the stem to dry up/die off after they have been open a while. It's not a cause for concern and it will grow a new one when ready to flower again.