This is the way I play this song (It is modified from the first version posted by 
 I thought the E chord in the bridge of the other version sounded really weird (and I like the 
of the B7 rather than the Bm a little better in the verse/chorus), so I changed them.

Intro:
G

Verse:


Em        C       G         D
If you're going to San Francisco,

Em         C        G                D
Be sure to wear some flowers in your hair,

Em        G        C        G
If you're going to San Francisco,

Em           B7        C             D
You're gonna meet some gentle people there.

Chorus:


Em        C       G         D
For those who come to San Francisco,

Em         C        G          D
Summertime will be a love-in there,

Em        G        C        G
In the streets of San Francisco,

Em     B7          C                D
Gentle people with flowers in their hair.

Bridge:


F              Dm
All across the nations,

F              Dm
Such a strange vibration,

G
People in motion,

F               Dm
There's a whole generation,

F          Dm
With a new explanation,

G
People in motion,

D
People in motion,


End: Repeat chorus


For those who come to San Francisco
Be sure to wear some flowers in your hair
If you come to San Francisco
Summertime will be a love-in there

A      C#m     D       A
If you come to San Francisco

A     C#m            E7      A
Summertime will be a love-in there