New Stratus Owner....Need some guidance

I just got a 2000 2.4L Stratus Automatic last week. I've been on vacation at Gatlinburg the past week so this is my first chance to post on these forums.

Here's the details:

Silver
Wheel Covers
6 speaker sound system w/ CD player
power seat, window, locks, mirrors
Body in perfect condition with no scratches in paint, paint is still very very deep and shiny.

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So my point is, I'm wanting to get into the customization of my car, but I don't want anything really ricer or street racer. Something that is nice, will make my car run nicer, smoother, and maybe have a little bit of a neat exhaust sound. Anyways, getting back to the point, what are some subtle, cheap, and worth-while upgrades to my car without screwing up my OBD II computer or anything of the like.

Thanks

you bought a 4 cyl. engine and want to tune it out to make it faster.... wrong car dude..buy an import