It probably depends on the terms of the bonus scheme as well as what is in your contract (so you may have to go back to old emails to find out what the terms of the bonus is).
Any bonus scheme should be easily measured- so if the term of the bonus finished (completely...rather than almost) prior to you leaving, I reckon you would have grounds to get the bonus in your last paycheck. BUT as mentioned above, companies can sometimes have certain exclusions whereby you must stilll be employed by the company of the date the bonus is due to be paid.
If it is a substanial amount, you will need to do you research and get as much of a papertrail as possible (as in emails, contracts, performance etc).
I doubt your current employer would be willing to keep you employed just so you get your bonus (as suggested by amtc). If you have offered your resignation and they have accepted it, they are not any obligation to re-instate you (AFAIS).