i have a Civic EX and put an AEM cold air intake on it. its looks great under the hood, sounds nice, and gained the car about 10 hp (and better gas mileage) they run around a couple hundred dollars and sometimes are slightly harder to put on.
short ram intakes are ok too, cost less and are easier to put on, but won't give as much of a hp gain. also im sure you can get a cheaper CAI than an AEM, its just the company i personally prefer