Welcome to the party.
Well, okay, couple things you should know. Firstly and foremostly, a lot of guys on here have a strong distaste for Volkswagen. You'd have to ask them why. I havent had much luck with them myself.
Now, with regards to the 318i... you've got yourself an awesome set of wheels. I've got a 325e (the six in-line) of the same year, and they are great machines. Depends how you want to turn them heads. Are you thinking appearance, or performance wise? On the performance side of things:
- K&N Air Filter/Intake: very noticeable improvement in response
- Performance coil/wires/plugs: Allows a bigger gap on the plugs, more power.
- New differential: there are a number of different kinds of diffs that can give you
better tire-burning, gut wrenching launches, but at the expense of higher RPMs on the highway. Choose your ratio wisely.
- Exhaust system. This DOES make a difference, especially in how the car SOUNDS. I've got a performance system on my 325e, I have to phone the last owner to find out what exactly it is, but it is a high flow setup with resonator, and it sure lends a lot to the car's persona. Cruising sedately, she sounds like a power boat burbling along. Open up the throttle and that burble turns into a feral roar. Makes the stock system sound, well, pissy in comparison. Plus the enhanced flow is good for some power.
- If you wanna go all-out nuts, find a good donor car with a 2.5L I engine in it (out of a 325i.... good for much power) and drop that in there, and do the same mods. Puts you in a whole different league. You could also find a 325e engine (detuned slightly, more economical, lower redline, but still lots of torque) for a bit less.
Now, on to appearance. You want to keep it stock, or do you want to go nuts on the outside? Every car reflects the personality of it's owner, I think. You could paint the bumpers, tuck them, stick on some ground effects, crosshatch wheels and stick a huge can on the back, but then you'd really be turning a fine German automobile into a Japanese rice rocket.
There's lots out on the internet, and even more ideas just looking at the cars owned by the people on this forum. You'll find your style.
By the way, if I hadn't said it yet, congrats on the BMW.