There are basically two options, which are vastly different, and it all hinges on the word 'she'. For the sake of simplicity, let's assume that the speaker is Shakespeare..
'And yet, by heaven, I think my love as rare
As any she belied by false compare'
Option 1 is the one Menimao suggested. In this case 'my love' refers to his beloved (as Miri pointed out), and 'any she' refers to 'any other woman'. Here Shakespeare would be saying 'although I can't write false romantic comparrisons as well as other men/poets (Marlowe or somebody perhaps) my woman/girlfriend/wife is just as good.' In this instance, Shakespeare is responding to the words of other men, and ends by justifying the quality of the woman whom he is in love with to other men. 'She' is merely a subject for discussion.
This depends on a usage of the pronoun 'she' as a noun meaning 'female', which, though unusual, is still plausible. It does seem oddly clumsy for Shakespeare though - 'she' in this sense is completely redundant, and could easily and more usefully been replaced with, for example, 'they'.
Option 2 (my prefered choice): In this case, 'I think my love as rare as any she belied by false compare' is taken completely literally. 'Love' means 'love', 'she' is used as a pronoun in the normal way and refers to one particular woman (let's say Shakespeare's girlfriend), and 'belied' is a verb in the past tense, of which 'she' is the subject. In this instance, his girlfriend has described her love for him in poetic ways that he feels are completely false (it's very easy to say 'You're perfect, my love for you is like the moon' or something like that - I've seen several million sickening valentine's cards over the last view days that do exactly that), and the expectation is that he will do the same for her. Shakespeare refuses to play the game, insisting instead that, though he won't pretend that she is perfect as she has done, his love for her is just as real as the love that she has said she feels for him. In this instance, Shakespeare is addressing his beloved, and ends by justifying the quality of his love for her. 'She' is the object of the poem, the one it is intended for.
The problem is, of course, that the translator has to pick one..
EDIT: I'd just like to make it clear that, tragically, none of those 'several million valentine's cards' were sent to me. Just before I sound a bit big-headed..
(Mi dispiace, il mio Italiano e' troppo povero a dire quello! E forse anche il mio Inglese..)