Agree with what Tony says, in general -- you should get an assignment of IP in place for *everyone* who is working on development -- this includes employees and consultants. (Note that this is different from an NDA, which is a promise not to reveal IP and other confidential information). Ideally that should be in place before they contribute any effort, to avoid any unpleasantness if they're not cooperative; though it's probably possible to make it apply retroactively (however IANAL).
However the complication that Lona raises is that the company isn't incorporated yet; so who would they assign it to? This is where I think you may need legal assistance. One possibility would be to sign something agreeing to assign it to the corporation once it's formed, though I'm not sure how you'd word that or make it binding (how would you legally define an entity that doesn't exist yet?). Another would be to assign it to you; then you would assign it (along with your IP) when you form the corp. Ask you friendly attorney.
Another issue -- you mention that no compensation was given. This often happens in startups, where friends and/or prospective co-founders do some work, just to help out or to see if there's a fit. But don't make the mistake of thinking the fact that they haven't been paid means their contribution is free -- as Tony says, they legally own it. And it's my understanding that in order for a contract such an assignment of IP to be valid, there needs to be an "exchange of consideration" -- i.e. they need to get something in return for their assignment. So you may need to pay them something (even if it's $1). Again -- IMNAL.
So one last bit of "paperwork to be signed to make sure no loose ends are left untied", if you really want to be comprehensive -- typically NDA's call for the return or destruction of all confidential material the person has received (or created) upon termination. So getting them to sign something saying they've done so (and re-affirming that they understand and agree to the future non-disclosure terms of the NDA) is the formal thing to do.