This is a C# minor major 7th chord - pretty unusual. It's the i chord from the harmonic minor scale.

Here's how it can be worked out:

I like to first move the chord to a more common root. On this one, let's move the chord one fret toward the nut, which gives us a C root. The notes are then C, G B and Eb. If we re-order the notes, we have C, Eb G and B. We know that C, E, G forms a C major chord. Since there's an Eb instead of an E, we've got a C minor chord. We're then left with the B. The last note in the C major scale is B, so we can say the B is acting as a major 7th. The question becomes, what the heck do we call the chord? It's not at all hard! we just call it a C minor major 7th (which sounds like the name of a character in Catch 22!).

Now that we figured out the name, all that has to be done is move the chord back to it's original position, giving us the final answer of C# minor major 7th.

As a check, let's now look at the notes in the chord. We've got C#, G#, B# and E. So, you are asking yourself "why in the heck did he spell the chord so strangely? B#? The answer starts which the key of C#, which has 7 sharps: F, C, G, C, A, E, B. This means the C# scale is written as C#, D#, E# F#, G#, A#, and B#. The minor in the chord makes the E# become an E. The last note of the scale B# (which is the enharmonic equivalent of C).

One last point: I noted that the this chord comes from the harmonic minor scale. This scale is the same as the natural minor scale (also known as the aeolian mode) with the 7th raised a half step. Going back to C minor chord, let's look at how the harmonic minor scale is constructed. The relative minor of Eb major is C minor. You can prove this to yourself by looking at the circle of fifths or check out Jason Smith's dicussion of the circle of fifths in the forum. To construct a C natural minor scale, use the same notes as Eb major and just start on C rather than Eb. The key of Eb has 3 flats in it (Bb, Eb and Ab) making the spelling of the Eb major scaleto be Eb, F, G Ab, Bb, C, D. The C natural minor scale is therfore spelled C, D, Eb F, G, Ab, Bb. Notice that the this looks like a C major scale except the 3rd, 6th and 7th tones are flatted.

Now we're almost there! As I said in what feels like an eternity ago, the harmonic minor scale is the same as the natural minor scale except the 7th tone is rasied a half step. This makes the C harmoinc minor scale be C, D, Eb, F, G, Ab, B. Let's now form the i chord of the C harmonic scale by stacking thirds on top of the C (just put every other note of the scale on top of each other). When we do this, we have C, Eb, G, B. Now compare this to the C minor major 7th chord described near the top of this overly long post and you'll see the two chords are spelled exacly the same.

The point of going into all of this harmoinc minor business is to show that the minor major 7th chord isn't just a random set of notes. It comes directly out of a the harmoinc minor scale.