[ebsameer]

I have drawn the following resonance structures for SO3-:

http://www.cartage.org.lb/en/themes/sciences/chemistry/inorganicchemistry/Informationbonding/bondingindex/Resonance/SO3.gif

However, couldn't I also draw3 more, since Sulfur does not obey the octet rule (thus forming more than 3 bonds)?

Extra 3:

O=S=O
    |
    O (-)


O=S-O (-)
    =
    O

(-) O-S=O (-)
        =
        O 

[Dan]

I have drawn the following resonance structures for SO3-:

*link*

Those are all representations of SO₃ (the neutral species).

Are you sure you want to be drawing structures for SO₃^- and not SO₃^2-?
SO₃^- would be a radical anion, ie one unpaired electron on S (whereas SO₃^2- has a lone pair on S, and SO₃ no lone pair on S).

Extra 3:

O=S=O
    |
    O (-)


O=S-O (-)
    =
    O

These are SO₃^-, you sould probably include the unpaired electron on S when you draw in in your work.

(-) O-S=O (-)
        =
        O 

Did you mean to put a minus charge here?