The harmonica is a much-neglected instrument that is actually quite enjoyable. I personally just started 4 days ago (that'd be Thursday, June 21st, 2001), and already I can play some recognizable songs. I have no musical talent whatsoever, so this is a big accomplishment. And you can do it too!

First things first: you need a harmonica. Specifically, a diatonic harmonica. Mine has ten holes (probably known as something fancier than 'harmonica holes,' but I'm not sure what they're called. See? You can learn to play it without even knowing anything about the instrument itself! Fantastic!). According to one of the tablature sites I found, you need a diatonic one because the other kinds (chromatic and tremolo) have the holes in different places and therefore won't work as well with their tabs. For example, the tremolo harmonica my mother owns has two rows of holes, and eleven holes across.

I believe the one I own is a concert pitched, or 'C' harmonica. I'm not sure if the tuning makes a huge difference or not, but to be on the safe side buy a 'C' harmonica. That's what the salesman told me, at least.

As far as brands of harmonicas, I know that Hohner makes some very high-quality ones. This information also comes from the salesman, and it's the only kind my general music-teaching mother has ever heard of. I'd imagine that there are other brands out there, though.

Okay, now for the fun part: learning to play your harmonica.

If you'll notice, your harmonica has numbers over the holes. If it doesn't, flip it over. If it still doesn't, you may be in trouble. But have no fear! Masking tape is here! Simply take a strip of masking tape and write the numbers over the holes. Blow into the harmonica first and make sure that the lowest-pitched note is on the left side and the highest-pitched note is on the right side. The lowest note is number 1 and the highest is number 10. If you got a harmonica with more than 10 holes (I hear 12-holed harmonicas are popular as well), then keep going until all the holes are numbered.

I play using harmonica tabs. These are simply numbers, either positive or negative, generally written over the lyric of a song. Frex:

       6   5   6    6   5      6
      This old man, he played one
      -6    6   -5    5   -4 5   -5
      He played nick-nack on my thumb
       5  -5  6    4    4  4   4
      With a nick-nack, paddy-whack
       4    -4   5 -5  6
      Give your dog a bone
       6   -4  -4   -5   5  -4   4
      This old man came rolling home
So, what does this mean? It's simple, really. The absolute value of the number is the hole played. If it's positive, you blow into that hole. If it's negative, you suck (known as a 'draw') out from that hole. That's all there is to it! Just blow and draw according to the rhythm of the song and you've got it!

This is, of course, just the bare basics to harmonica playing. There are more difficult techniques to master, such as bends and 'wah's with your hands, but for simple, easy harmonicing, this is all you need!

Some tablature websites for your perusal:

      Over 650 songs for the harmonica!
      Another good site, with online lessons as well

      Not as many tabs, but still a nice site
Happy harmonicing!