No candidate who has not won plurality of delegates in at least 5 states can be nominated from the floor. So forget about anyone else being nominated except those who actually competed in the process.
Maybe I am wrong but the case is at this time that on first ballot Romney will be nominated and Ron Paul could be also nominated by five of those states that are said to have been won by Ron Paul according to delegate sum. Scenario: Romney does not get 1144 on account of Paul's, Gingrich and Santorum delegates no voting for him. Ron Paul may not get 1144 either. The Convention is said to be a Brokered Convention. At that time 5 states delegations can support another candidate such as Sarah Palin, Paul Ryan, Rand Paul, Jeff Bush, Barbour, etc. etc. and if so, that person can get nominated to compete also against Romney and Paul. Usually a deal is made with a Vice President in mind. Usually when a nominee is not accepted, say Romney is denied, a deal is forthcoming usually regarding a VP or some other concession. But I can be wrong.