Houston "spicy" burger
i like spicy burgers too.
if you want to go nucular, the conversation begins and ends with the firehouse burger at lankfords grocery in midtown. it has minced up habaneros in the patty and it will make, or perhaps ruin, your afternoon.
if all you want is a little heat and some special flavor, there are many less spicy options.
the chorizo burger at taco milagro is good. the patty itself is less than stellar(dry and small), but the addition of chorizo brings some heft and grease and the overall burger is of good construction. you can get it with or without peppers. i also think it goes well with their black salsa.
the torta-burger at tortas el angel is fantastic. what they do with their cheese on the grill is special. have them add an egg and jalepenos, and if that doesnt do it, douse it with the green tomatillo sauce to get the heat up. the torta buns are nice and soft.
the chapli burger at himalaya is a delicious little south asian slider (search the houston press site for robb walsh's report on this). its not the spiciest thing out there, but it has a nice mix of foreign flavors. im sure if you request, they could get it as spicy as necessary for you, it is, after all, an indian/pakistani restaurant.
and, since spicy burgers are your thing, if you are ever in austin you need to try the amarillo burger at casino el camino on 6th street. grilled serrano peppers layered all over one of the best patties in town. amazing burger.
Around here the most usual thing would be to request jalapeno slices on the burger. This will be available at lots of places. Some will also have hot sauces to choose from.
Tornado Burger in Stafford on FM 1092 has a spicy burger I think they chop up jalapenos and mix into the meat. It doesn't do it for me.
I'm try to think there's some other place I've been to that does that but I can't remember it now.