The natural next step is a PDA. Perhaps you could use this type of system to model an AI that can get distracted or become faced with an intermediate task and then return later to the original objective?
For those of you who don't know what a PDA (Push Down Automaton) is, it is basically a standard finite automaton but with a stack that you can push things to and pop things of -- you can then react differently if you get input a in state B versus getting input a in state Q.
Many parsers make use of PDAs when they parse source code.
I've used PDA in games A.I. programming several times too. In fact I'd be surprised to see anything beyond a casual game that didn't use high level 'task stacks'.
