Okay, right off the bat, I admit that my knowledge of music theory is...lacking. I was just curious as to how to go about learning about creating harmony. I have several riffs that I've been working on which require harmony, and I'm simply clueless about how to find that sweet harmonic sound. Are there charts for harmony? Specific theories? I need advice on where to look and what to look for.
I do believe that you use intervals..........but Im not entirely sure, ill wait for others to back me up if Im right....

My things:
Bowes SLx7
Washburn WG587
Washburn X40Pro
Washburn X50
Washburn HM24
Washburn WR150
Laguna LE200s
Arietta Acoustic
First Act
Valveking 112
VHT Deliverance

actually i wouldnt mind some answers either im stuck on harmonies as well >.<
screw around with different intervals, there are a few different ways of approaching harmony.
make Industrial and/or experimental electronic music? Join my group!

learn intervals. learn what a 3rd, 5th, etc means.

without getting too technical, heres a more laymans term for the intervals for harmony:

unison/octave - the same notes, most stable, unison when harmonized with all others can create an awkward spot
5th - basically a power chord interval, sounds fine to momentarily hit but consecutave notes harmonized with 5ths sounds odd
4th - very similar to a 5th because going from the 4th to octave is a 5th. could say an inverted version of 5th.
3rd - very harmonious, makes distinctioins between major and minor tonality. easiest to harmonize with.
6th - same relationship that 4th to 5th has
2nd/7th - very dissonant as they usually are a half/whole step away, used more with complex chordings

start with 3rds and try and throw in 4ths/5ths and 6ths into the mix, work towards making contrapunctual harmonies, independant melodic lines that intertwine with eachother that are still harmonious. straight 3rds is very boring and quite overused. carry this concept over to chording and melody as well.

listen to some melodic death metal for great examples of harmony.

here is a great example of harmony:


listen especially on the slow parts. in flames also has some great harmonies as well.
What kind of style? Thirds are a pretty popular harmony choice, especially in metal. If you know the key of the riff you are playing, all you do is just go up 3 intervals from whatever note you are playing in the scale. For example if youre playing something that goes 1 4 6 4 the harmony with 3rds would be 3 6 8(1) 6. If you dont know basic scales, then youll have to rely on your ear, which if you don't know scales your ears probably untrained and you should just learn scales. They're really quite easy to learn.

EDIT: just listen to the post before mine, its a lot better
I haven't pulled the "Theory Sticky" thing in a bit, but it does have some good information on harmonizing.
1 2 3 4 5 6 7 8 9 10 11 12 13 14
1 2 3 4 5 6 7 8 9 10 11 12 13 14

Hope that helps
5150 III 100W, Mesa 4x12 Cab, Framus Cobra Cab, M-Audio Profire 610, ISA One Pre, SC607-b, Equator D5's, Countryman Type 85 Di box, Radial JCR, Superior Drummer, SSD 4 Ex, TS9, NS-2 and the list goes on and on