I bought my 2001. 5 in September of 2001, so they will still be around for a while. But your choices do start to get smaller the longer you wait. Got lucky, I found mine.
I like the look of the new 3500's, but am not too crazy aout the 2500. If I was looking for a 2500, it would be a 2002 for sure. 3500, not so sure, but probably the 2002. Like stated before, tried and true (with the exception of a few little bugs). I'm sure the new models will be good trucks though.
Brian