Before continuing, I strongly recommend taking a look at the following website.  The owner of this page knows lighting technology and has a lot of good things to say:

Daniel Stern's Lighting FAQ

If you're living in the United States (and possibly Canada), your car came from the dealer equipped with DOT-spec headlights.  With some newer cars this isn't much of a problem (see the above FAQ), but if yours is from the '80s or earlier, chances are you've already noticed how terribly inadequate your forward lighting is.

There are a couple of options.  The first (which also happens to be the easiest and the cheapest) is to locate higher wattage bulbs or uprated sealed beam units.  While there is no argument that this does offer some improvement, it isn't a terribly good solution.  Aside from potentially damaging your wiring harness by drawing too much current across it, this solution overlooks the real problem:  The fundamental reflector design of DOT-spec lighting, quite simply, sucks.  All you really end up doing is increasing the size and brightness of that poorly focused blob of light that's projected in front of you - it won't improve your light distribution one iota.

The second solution is to add some form of auxiliary lighting.  Although not necessarily the cheapest route, the good news is that Saabs come from a land where nighttime road visibility is poor in many (if not most) areas, and Saab has taken steps to facilitate adding extra lighting.  All Saab 900s (and 99s & 9000s, for that matter) have mounting locations for under-the-bumper lighting.  These positions are best used to mount foglights due to their elevation, but they can also be used to hang driving lights from manufacturers such as Bosch or Hella.  On earlier 900s (1986 and earlier) you can actually flip the mounting brackets upside down, and mount lights above the bumper - lights such as the Hella 500 are great here, since they are perfectly sized to clear the hood opening.  If you're truly ambitious, you can actually mount lights above and below the bumper as I have on my 1980 900T; those are Hella 500s (driving lights) above the bumper, and Bosch Pilots (fog lights) below.  

The third solution, which offers the single largest improvement but also happens to be illegal in most states, is to replace your headlight assembly with European specification (H4) units.  On earlier cars, the H4s replace the sealed beam and the plastic bezel with integrated parking lights, on later cars there is almost no visual difference between DOT and H4 style lights.  H4s offer significantly improved light distribution for safer high-speed driving, and have a very sharp vertical cutoff to reduce (if not eliminate) glare for oncoming drivers.  Additionally, factory H4s have a lens, reflector, bulb, and housing which can each be replaced independently, meaning a rock chip or worn out reflector won't necessitate replacement of the entire headlamp.  H4 bulbs can be purchased nearly anywhere, as they've been in use in the U.S. forever on motorcycles and off-road vehicles.  Installing these lights is easy - they slip in where the old ones come out.  On earlier cars, there is no wiring to do, as the old sealed beam connectors plug directly in.  On later cars, you will be required to do a little work, as their 9004 bulbs use different connectors; the easiest solution is to snip a few inches of wiring from a 1986 or earlier 900 at your local junkyard, then splice it onto your wiring.  It takes a few moments, and Saab was kind enough to use the same wire color coding throughout the entire run of the 900 so you don't have to do any tracing.

One note:  Hella does sell H4 units which will directly replace the sealed beam on 1986 and earlier 900s (as well as just about every model prior).  While these are a marked improvement over the standard lighting, they are not the same as the real Saab-specific H4 lights.  You can find them at many auto part stores, and cost under $50 per side.  If you're having trouble finding someone to sneak you a pair of real H4s across the Canadian border (where they got the real deals), these might offer you an alternative.