To eliminate the cell light:
Catless - Only with ecu tuning
100cpsi cats - Only with ecu tuning (bungs extenders may work in some cases: -08 models, type of mufflers...)
200cpsi Cats - Ecu tuning or bungs extenders.

Notes:
1. Stock exhaust system has 600cpsi (cells per square inch) cats with four O2 sensors, 2 before and 2 after the cats. The first O2 sensors (before the cats) give to the ecu all the info for the management of the engine. The second sensors only give the info about the cats eficiency (emission control). The cell light due to the cats don't affect the performance of the car. You can drive it with it on without any worries.
2. HJS and Emitec has a special cats (100 and 200cpsi) that don't throw the cell light. Due to its "S"-form cells it provide better O2 readings while maintain the same(/higher???) free flow than the normal cats with square form cells. The most trusted companies prefer these cats because it guarantee trouble-free with the cell light. Once it is more expensive than the normal cats, this is one of the reasons why their exhaust are so expensive ($4000-$6000).
3. Any ECU Tuner is able to eliminate the 2nd O2 readings (the ones that throw the cell light due to catless/free flow cats system) - RUF, FVD, GIAC, Promotive, Softronic, Techart, Gemballa, Speedart...

 

With a good exhaust you shouldn't have to disable the CEL.

 

+1 my 200 cel cargraphic needed no ecu tweaking or bung extenders.

 

Tiago, Good info but you never want to eliminate the 2nd O2 readings. You only want to up the rear O2 tolerances. You want them functioning in case of a more serious issue. FVD never eliminate's them entirely unless specifically asked to do so.

 

Thanks for clearing up things Rhonda.

 

Thanks for clarify this. I guess that all depends of the goal, but is good to know that you reach everyone needs.

 

with 200 cell cats, you don't have to worry about the CEL. Only with 100-cell cats.

For 100-cell cats, you will need an ECU flash to get rid of the CEL.