Taillight blackouts is a common "first" mod for a lot of people. The reason naturally is the quick and easy install with an immediate change in appearance. I got these shortly after I bought the IROC. Although I bought mine used from a fellow board member - they are fairly inexpensive.

The install is simple and includes attaching the supplied stick-on velcro tabs. I suggest taking your time when you mount these. Remember, the tabs show at night when you turn the lights on, so put them in the least visible locations. However to ensure that the covers stay on, it is also important that you place the tabs wisely.
First, wash of the lights real well with a good cleaner such as an alcohol pad. I also found that the tabs were unnecessary wide, making them show up too much at night. So, I split them in half and placed them along the edges. Be sure to put two on the black filler piece, one around the corner towards the licence plate and on both sides of the very outside corner of the light.
Also remember - place the tabs on the taillight FIRST - not on the cover!

If you want to buy these covers, check out Summit Racing and also eBay for used covers.

Note: Depending on your local laws, blackouts may not be leagal in your area - so be sure to check that out as well, if you are concerned about getting a ticket!