Full exhaust, long tunbes, Y-pipe and a good 3" catback. The Pullies will gain you very little, mainly just throttle response, the manifold spacer also seems to give a very minimal gain (on the dyno atleast) but those are options too.
In all honesty, if you add up what all of that will cost (almost 2k by my math, without even getting into a trac bar, slicks or a map3/x-1 etc) and consider the gains in comparison to that cost, it's really not worth it IMO. All that cash and you'll still be in the mid 14's, provided you can actually drive.
Spend that kinda dough, plus what you've already spent on certain OTHER vehicles, and you can go much faster. Also take into consideration that for that kinda money, you're spendin almost half of what it would cost to boost your truck and then you'd just end up buyin all that other stuff afterwards ANYWAY and you'd see better results from those mods if you WERE boosted.
All this is the reason I'm not gonna spend big bucks for small gains on my truck. I'd like too but it just doesn't seem logical to me anymore. I say boost if you got the cash, or get another vehicle with better (and cheaper) aftermarket support if you're truly serious about speed.