well of course theres always +2,+3..
in reality there is no real 'highest number'. there is infinity, which is not a number but a concept of never ending. if anyone ever finds a very large number, you can always add one and you get a larger number.
so anyone asks you the largest number, tell them there is no largest number, because you can always get 1 more by adding. however there is infinity showing the concept of never ending.
hope this helped. look at the link below for info on infinity.peace
http://en.wikipedia.org/wiki/Infinity