:hi:
Congradulations on your pending purchase. There are a TONNE of headlight mods available for the Focus, and I'll try to explain a few of them to you so you can get an idea of what you think is best for your car.
Silverstars:
This was mentioned above, and are by far the easiest and cheapest mod that you can go with for your headlights. Essentially all you're doing is changing your bulbs to a brighter white light. The benefits of this are debateable, as no one can really decide as to whether or not they really project more light, but either way they look kickass. You're looking at about $40 for this.
Headlight Covers:
These are pictured in my signature pic. A very cost effective mod that adds a lot of style to your car. These are easily installed using adhesive strips, and are made of plastic. They are great because they protect your stock headlights from stone chips and other things along those lines, but they cut down the light output by about 75 - 80%. This can be overcome with brighter fog lights but eitherway, it's not a good idea if you're planning on driving out of the city. They can of course be removed and put back on whenever you like.
Projectors:
A lot of guys have gone with this mod, and most of them swear by it. Among the most notable on this board that have done this are ZX3TUNR, Darkpuppet, Flofocus, and others. Flo's car is pictured below. The thing you have to be careful of when doing the Projector Light mod is what brand you pick up. There are several cheap Ebay brands that you can get for about $90 or so, but you would be advised to go for the good ones. The most popular brand that most people stand by is Hella. These are reliable, and when properly aimed and installed, can dramatically increase the light output of your vehicle. Some people love em, other's hate them. Your call to make really.
Euro:
If you post here regularly you'll soon come to realize that we love Euro parts in Canada. I think it's safe to say that these are some of the coolest lights you can go with. With integrated turn signals, seperate high and low beam bulbs, and OEM fit, you can't really get much better (except for the next one I'm about to mention). They come in a couple styles, depending on which model you buy... some have grey surrounds, some have chrome... either way they kick ass. Take a little to get them wired correctly, but the guys on here can help you with that no problem. Expect to pay a pretty penny for these... the lights will be expensive, but bug ZX3Tuning aka Mitch to save a buck or two on shipping.
HID's:
These are the best of the best. High Intensity Discharge lamps, just like the ones as seen on BMW's and Mercedes. These were featured on a limited edition car in the states known as the Sony MACH edition Focus... but a couple guys on here managed to grab the lights right off the bat. Nowadays they go for about $1000... but you get all the wonderful advantages of high intensity discharge, such as the ability to piss drivers in front of you off, and impressing all of us with how deep your pockets are. There are integrated turns in these as well as driving lights...uber sexy..
(This is 2001ZTS's car... the pic is too big so here's a link)
2001ZTS with HID's
Hope this helps you make a decision. The options listed above are not the only ones you have.. there are a huge number more, but these are the most common/most recognised. Take a look, post what you think.