Plugs: Word on the street is that the stock plugs are the best ones for stock applications. I remember asking about Bosch +4 Platinum plugs and the general consensus with our more technical members was that they weren't worth it.
Oil: Mobil 1 and Royal Purple are good oils, but just remember when you move to synthetic you can't go back. Always go with the owners manual on what oil to use, not brand but the weight and grade etc.
Performance: As Midas78 already stated, there are a lot of free mods. You can cut the bottom of the stock airbox out for added performance and a better performance sound. The best all around performance mod, even though I'm not experienced with it, would be the X-Cal tuner. It tunes the shift points of the transmission, reprograms the PCM for added horsepower, etc.
Lighting: If you decide to clear the headlight corners you need to look for grey glue sealant, black will not work. When you clear them, you'll need Orange or Chromium 3157 turn signal bulbs to make it legal. I'd recommend Chromium bulbs. They are priced around $10 a set, and they don't make your corners look like, as Ken Garrison says, egg yolk.
