What type of force holds my body rigid & doesn't make it collapse?
Adding on to what Martin said. If you imagine an atom to be the size of a football stadium, the nucleus would be the size of a fly on the fifty yard line. The vast majority of an atom is empty space.

In the 'classical' view, atoms are mostly empty space and the reason they feel solid is that if you try and push them, the electrons around your atoms bump into the electrons around the other atoms and because they're both negative they repel each other and push away. You feel this force as 'solid'. It's like pushing a really, really stiff spring or trying to force 2 magnets together, except it's electronic in origin. 

In quantum physics, each particle has a wave function. Wave functions can only exist in certain forms, and when electrons are bound in an atom their waves spread up over a big volume (it's the only way mathematically to get a stable wave, ie an electron that exists. Since it exists, its wave function spreads out much further than the thing you classically think of as an electron). 

Electrons have something called antisymmetric wave functions, which means they obey the Pauli exclusion principle: 
http://en.wikipedia.org/wiki/Pauli_exclusion_principle

You can't have 2 electrons in the same state (and 'state' includes 'space'. You can have 2 oppositely spinning electrons, but no more in the same place). So atoms spread out because you can't squeeze the wave functions in. The rest of it is electrostatic repulsion just like in the classical model. 

I'm sorry if that sounds a little complicated, but it's a combination of quantum physics (which doesn't really make sense, even though it works!) and electronic repulsion (from like-charges-repel).