People seem to be forgetting the subject here. What mods can you apply to your car...
Warranty aside, there are several things you can do that don't involve the overrated and overdone engine swap or turbo install. Start with the basics...
A good exhaust system - if noise pollution is a real problem, then go with something like the Apex'i World Sport system. While it doesn't give you massive gains, it would be a good start.
Intake - Again, it's not going to suddenly mutate your car into a beast, but you're going to need good air flow on both sides of the engine before you dig in anywhere else.
Chip - A simple addition that can go a long way. I have yet to do this myself, but I have yet to hear badly about it.
Electronics - Give your car a better power system. Stronger wiring, better grounding and a better alternator will help out in the long run, and it makes sense if your engine has a mid to high powered stereo to contend with. Upgrade the ignition, plugs, wiring and anything else that aids the spark.
Suspension/Chassis - The engine can only do so much. You need to be able to get whatever power you have to the ground in the best way possible. A good set of coilovers is a good addition, as well as anti-roll bars, better control arms and anything else that stiffens the chassis and keeps the wheels in contact with the ground.
Drivetrain - This depends on what you have. If you have a 5 speed, a flywheel, new clutch and short shifter would be great improvements. If you're going with an auto, re-valving the torque converter, or just swapping out for a better after market one, is the way to go. The torque converter hogs sooooo much power and keeps the engine and wheels from fully connecting to each other. As with a manual, the lighter the rotating mass, the better.
Tires/Wheels - You don't need slicks or anything like that. A good tire like the yokohama perada is great for daily driven speeders. A lightweight wheel is also the way to go. And please...please please please let's not have anymore civics with twenty inch "bling blings."
Engine Internals - This is where you begin diving into the deep end of the pool. Stronger rods aren't really necessary. Higher compression pistons are great, and the forged type are even better...they resist expansion under high-heat conditions so your piston clearances can be tighter. Engine coatings help out a lot. They don't really give you and power gains, but the engine will run better, and efficiency = power in my book. A good head port will get you a little more. All of these are great mods if you plan on throwing a turbo in later on, but if you do, keep in mind that you'll need to take out those high compression pistons...bad things can happen.
Weight - lighten the car...kick your friends out
I'd drop everything in the trunk (spare tire, jack, etc); only you don't want to throw your car off balance. Ditch the heavy amps and subs and anything else you've got in the car that you don't need.
Fuel - User higher octane fuels, and try to match the fuel consumption to the amount of air that's actually getting into the combustion chamber. Too much fuel and the engine will bog. Not enough fuel and you'll end up with some mild detonation problems. A new fuel pump, filter, rail and injectors are great additions here. Fuel management isn't necessary, but is great help during the tuning stage.
Electronics - Not much to add here. Maybe the fuel management mentioned above, and if you've got VTEC, take advantage of it!! A VTEC controller mixed with some of these mods coupled with a really good fuel controller is almost like having a turbo without the added engine wear.
Aerodynamics - Please don't throw one of those gigantic aluminum wings on your car...at the end of the day, it's a civic, and unless you're running in the ITC, it's pointless. The stock civic wing will do a good enough job. A front lip spoiler or wind splitter is a good idea, and anything that keeps air from getting under the car is good too. Right now, my friends and I are working on an air diffuser for use under the car. Nothing complicated, just something to ease out the turbulence under the car at speed.
The D16 may not be the cream of the crop, but it ain't that bad either. While we all dream of H22's and B20's, I take more pride in having a strong overall engine than a struggling beast that's too powerful for it's own good. No dis to anyone else out there...I happen to love forced induction civics that eat supras and vettes for breakfast...but having a strong car that retains it's stock appearance is often more fun than a car that flaunts everything and then gets beat by the mini-van wearing two donuts on the front. <purges NOS system, revs and let's the blow off valve whistle...drops the hammer and breaks an axle...no fun at all> Talk back and list any other good mods you can think of.