The version of the opening credits that you'll be familiar with depends 

on your age (sorry!). I remember the late '90s version 

which had these lyrics:

   -6      6

Neighbours

5  -5 6  -6         -7       7       8       -8

Everybody needs good neighbours

  -8    8  -8  7   -6  -5  -6   6  

With a little understanding

   5    -5     6     -6      -7   7      9

You can find the perfect blend

   -6          -7         7      -10      9 

That's when good neighbours

   8      7     -8       7

Become good friends

Some eras have an extra two lines:

   -6      6

Neighbours

5  -5 6  -6         -7       7       8       -8

Everybody needs good neighbours

  -8    8  -8  7   -6  -5  -6   6  

With a little understanding

   5    -5     6     -6      -7   7      9

You can find the perfect blend

   9      -9

Neighbours

   8        -9     8      -8    7    -7  -8    7 

Should be there for one another

   -6          -7         7      -10      9 

That's when good neighbours

   8      7     -8       7

Become good friends

The full version of the song has an extra verse and a key change from G to Ab, so you'll need two harmonicas to play it. Here are the full tabs if you want to give it a try:

Intro:

-4 -4  4  4    -4 -4  4  4

5  5 -4 -4     5  5 -4 -4   

 -6        6

Neighbours

5  -5  6  -6       -7         7       8      -8

Everybody needs good neighbours

  -8  8   -8   7         -6      -5     -6     6  

Just a friendly wave each morning

   5       -5     6    -6 -7   7    9

Helps to make a better day

   9       -9

Neighbours

   8      -9   8  -8    7       -7     -8     7 

Need to get to know each other

   -6      -7    7  8  -8 -6  8  -8    -6   -8

Next door is only a footstep away

   -6      6

Neighbours

5  -5 6  -6       -7          7      8       -8

Everybody needs good neighbours

  -8   8  -8  7    -6   -5   -6    6  

With a little understanding

   5      -5     6    -6   -7    7       9

You can find the perfect blend

     9      -9

Neighbours

      8     -9      8      -8    7    -7  -8    7 

Should be there for one another

    -6         -7        7      -10     9 

That's when good neighbours

   8      7     -8         7

Become good friends

[KEY CHANGE]

  9     -9

Neighbours

   8     -9   8  -8     7        -7    -8   7 

Need to get to know each other

  -6       -7   7  8 -8 -6   8  -8    -6    -8

Next door is only a footstep away

   -6      6

Neighbours

5  -5 6  -6         -7       7       8       -8

Everybody needs good neighbours

  -8    8  -8  7   -6  -5  -6   6  

With a little understanding

   5    -5     6     -6      -7   7      9

You can find the perfect blend

   9      -9

Neighbours

   8        -9     8      -8    7    -7  -8    7 

Should be there for one another

   -6          -7         7      -10      9 

That's when good neighbours

   8      7     -8       7

Become good friends

     -6        -7        7      -10     9 

That's when good neighbours

   8      7      -8         7

Become good friends