To begin with, as you may know, the guitar has six strings each with a name. From low/thick to high/thin it is.
E/6th
A/5th
D/4th
G/3rd
B/2nd
E/1st
Easily to remember by the phrase: Eddie Ate Dynamite, Good Bye Eddie. This ofcourse only applies to normal tuning.
In musical language you have 7 normal notes: A,B,C,D,E,F,G and after that you start again on A, only it is an octave higher then the previous A. In between most of these notes there are half notes higher or lower which with most notes result into having a sharp/# (if you go up a half note) or a flat/b (if you go down a half note).
All notes in the musical language are: A, A#, B, C, C#, D, D#, E, F, F# and G. Or going down: G, Gb, F, E, Eb, D, Db, C, B, Bb and A.
Between B and C and E and F you don't have those sharp or flats. These are still a half step apart but a whole note apart, remember that. Now returning to your guitar.
When you hit your open string, for example your sixth/low E string, your note is E. When you go up one fret on the guitar you go up a half step. So going to the first fret on your low E string the note will be F. If you go up one more fret your note will be F# and so on.
When you do this on a different string this principle will apply as well ofcourse. When you are tuned differently from the standard tuning you start counting from the note your string is tuned to.
A good way to quickly get to know all notes on your guitar neck is to learn Cycle Five. I'm sure Guitartricks has a lesson for that. Apply Cycle Five on every string and practice it for a week and you should know a whole lot.
Edit: I did a bit of research and saw that Christopher Schlegel has a lesson on this. It is called the circle of fifths. You can find it here: http://www.guitartricks.com/lesson.php?input=13697
In my opinion knowing the note you are fretting is more valuable then reading it from the normal notation above a TAB. In this way you won't get stuck when you have no music sheet or TAB only without the normal notation above it.
Hope that helps!
JJ