List the first 20 friendly number pairs

APL (50)

↑⊃,/{g/⍨{=/{⍵÷⍨+/z/⍨0=⍵|⍨z←⍳⍵}¨⍵}¨g←⍵∘.,⍳⍵-1}¨⍳936

The list is slightly different but oeis.org agrees with me.

Output:

 28   6
140  30
200  80
224  40
234  12
270  84
308  66
364  78
476 102
496   6
496  28
532 114
600 240
644 138
672 120
700 150
812 174
819 135
868 186
936 864

C (132)

x=1,e;float d(a,b){return b?1.f*(a%b==0)*b/a+d(a,--b):0;}main(){while(x<1148)for(e=x++;--e;)d(x,x)-d(e,e)||(printf("%d,%d\n",e,x));}

Thanks to shiona for the ideas on shorter code. And Felix Eve for the Code(counting down makes more sense if you only search pairs). With the added Pairs even shorter.

Readable Version:

x=1,e;

float d(a,b)
{
    return b?1.f*(a%b==0)*b/a+d(a,--b):0;
}


main()
{
    while(x<1148)
        for(e=x++;--e;)
            d(x,x)-d(e,e)||(printf("%d,%d\n",e,x));
}

Ruby, 90 characters

h={}
1.upto(1150){|n|s=0
1.upto(n){|x|s+=x if n%x<1}
r=s/n.to_r
p [h[r],n] if h[r]
h[r]=n}