L, or LS/GS?
If you replaced the amp on the LS/GS syste, with an aftermarket amp, then I would say any higher end brand speakers will be good. I personally use Diamond Audio HEX series with silk dome tweeters. Focal, is also another good high end speaker. If you keep the stock amp, I would say one of the 2 ohm aftermarket speakers like SoundStream.
If you have the L, then any good efficient speaker will be Okay.
If you add an amp to the L system, then I would say any of the high end speakers I mentioned for the LS/GS system will be good.