What about "This is the last time I am going to talk about this"Originally Posted by navi tasan
All the above mentioned - two of yours and one of mine- are correct. Their use, however, depends on the situation and context in which they were or are used.
If you have previously decided not to talk, use going to +inf.
If you have just decided not to talk again, use I will.
If you have talked several times and found out that no use of keeping on talking about it, use I am talking