Welcome to the site. There several very good threads on where to start your path to modding. Where you begin your odyssey will depend on your ultimate goal. Some people start with audio, some start with lighting, and some start with performance. I would suggest looking at the signatures of the members. They are a smorgesboard of ideas for mods.
2007 LT 2.2
GMPP Air Intake * GMPP Extrude Honed Manifold * GMPP Cat-Back Performance Exhaust * Vibrant D/P * Jet Stage 2 Module
MOBIL 1 Synthetic Oil * DC Sport Strut Tower Brace * Color Matched Mirror Covers * EuroAntenna * 30-15 3M FX Tinting
Bridgestone Potenza Pole Position RE960AS on Premium Wheels
2.4 Intake Manifold Conversion * 2.4 TB * TUNE