i like 400exs. my buddy has one that rips mine up every time. and mines pretty damn built. i think if i do a 240, i oughta be able to keep next to him though.
the suzukis are great too. both suzuki and honda make a very reliable and finely tuned machine.
as for quick and easy torque. i'd say that having the head milled is sorta like just a quick bandaid. if you're gonna spend the money to have it shipped to a builder (like flotek, wildcard or kennedy_power) and milled, you're just throwing away money that you should spend on actually having the head redesigned. the stock head is retardedly out of whack. the squish parameters need to be changed and the deck leveled (a lot of blaster heads are crooked). just milling it down leaves you w/ the same squish numbers that suck. spend the extra little bit of dough on the redesigning.
also, the timing is a great idea that's almost completely free.
dropping teeth in the front sprocket or adding em to the rear is a cheapo way too.
i'd say the most important thing to making your engine run better would be the pipe. but not cheap.