a chromatic harmonica
a chord harmonica
this Chord Harmonica can play very much every kind of chords:minor, major, sharp, flat, even seventh...
But yeah! nothing interests me more than the diatonic. The Diatonic harmonic is more difficult to play well with tecniques and missing note that you have to figuer out to make a good solo. Each Diatonic harmonica only designed for a few among of chords, like the C harmonica can solo at the C, G, D(maybe) major chord,the diatonic harmonica is just for blues or rock n roll music so it plays very well on seventh chord and rarely on minor chords. With a diatonic harmonica, you can think of your own harmonica solo quickly with the right song,right chords, using various techniques like bending notes, wah wah, the train... everthing that fits the rythm and the chord.
So have a harmonica (10$ or 20$) and have a great time, you can perform with other intruments (usually guitar) by using the harmonica holder. so you can play the guitar for the chord, sing for the melody and play the harmonica for the solo, the chicks are gonna like it XD
I can play the harmonica, not so good but I know a few poppular techniques that I will show you in the note of the near future.
Here are some examples for songs wich has harmonica playing: