I ask my wife what she wants to drink next - if she has no preference, then I worry about what I want.
After that, I try to make sure that I am brewing in time for seasons and events. Atm my thoughts are turning to what beers I want to have around and on tap over Christmas - I always take a few kegs away with me when I head North for the annual x-mas pilgrimage.
In November I will put down an Aussie Pale ale so its ready for Australia Day 09 - In January I will brew an Irish Red or Dry stout for St Pat's Day - In Feb a chocolate beer for easter - you get the picture. Also if I have any beers I particularly want to enter into the competitions, I will brew them so they are (hopefully) at their peak in October.
I fill in the gaps with whatever takes my fancy. At the moment I am on a bit of lager kick.
I do like the notion of just brewing the appropriate beers for whatever VSS yeasts come out from Wyeast. You never know where you'll be going, but its bound to be interesting.
Thirtsy