The interior is probably the place you will be spending most of your time (driving it around) so isn't it only right that you sort it out so that it becomes more comfortable and looks nicer for you? Detailing the interior really depends on your personal view of what is nice and what is not... Some will like to keep their interior in stock, while some would like to have a busy, completely re-designed cockpit... It all depends on your personality and what you like...
In this section I will put up a few ideas, but in no way is this a restrictive
list of what you can do... Let your imagination run free and do whatever
you think looks nicer, feels better etc...
Some cars come straight from the factory with wooden dashes, and usually these do not need extra work... Most however, come with plain and ugly plastic dashes that may look nicer covered up. There are a few companies that produce ready made sets for your vehicle, and they usually come in a variety of different colors... for example you can have Burlwood, black Carbon Fibre etc etc... All you need to do is stick them in place (they are usually adhesive).

If you cannot find a good set that suits your vehicle, a few auto-accesory shops can design it for you... Here you have a choice of what color and material you want etc... Usually this turns out to be a very good improvement to the whole interior of the car and makes it look a lot more classy...
Other than using plain wood dashes, some people let their creativity run wild and experiment with chrome pieces (like the new M3 interior), leather or even different cloth materials with funky designs etc...
Depending again on the original look of your car, you may want to get a nicer looking steering wheel... Thousands of designs out there guarantee that you will get what you are looking for. Whether they are leather coated, futuristic design, racing-style steering wheels or anything else, you can proabably find what you are looking for.

One disadvantage of most aftermarket steering wheels is that they do not accomodate any space for air-bags... So if your car originally came with an air bag it will kind of make it useless... There are a few companies that make airbag steering wheels but these are usually pretty expensive and hard to find...

Not very expensive to have tailored to your own
car, yet these make a much better looking interior, dash mats are a very
popular application. For many popular cars you can even find these ready
made...
These come in all sorts of shapes and designs... Whether you want a plain floor mat to stop dirt from getting to your car, to whether you want a 'batman' dash mat, almost every design is available.
I personally find this a very nice touch, especially if the rest of the car is tailored to suit the floor... Coating the whole floor with aluminum gives the car a very unique touch, and gives off images of proffesional race cars. Having this done is usually pretty expensive, so what some people do is buy specially made rolls of aluminum that can be fixed to the floor of the vehicle. They usually present the same look if done well...
There is a lot you can do here... Car seats are basically made of springs and all sorts of wierd materials, and finally covered with the cloth or leather you actually can see. If your seats originally came as cloth, you can replace that with leather (the seats would be stripped and then re-covered). Also, even if your seats came in leather you might want to change it (to a different color, because the leather is aging etc...). Or if you wanted to just have a small design or logo imprinted on the seats that is also possible.

Some people decide to replace their seats completely. They either fnd
more comfortable or nicer looking seats, or go for the racing look and
put Recaro racing seats in there...
The background of your gauges are usually black and illuminated right? Getting White faced gauges are pretty popular mods these days, and are not too expensive or difficult to install. Indiglo gauges are also available for some vehicles. The picture shows you what the indiglo gauges look like in the morning and at night time:

If you want to go all the way and have a lot of money to spend then you can replace the entire dash with the gauges and get a set of custom-made dash kits that resemble those found in the new Volkswagen cars like in the image below.

The original gear stick that comes along with your vehicle can be replaced. In fact all you are doing is replacing it's cover. These come in all shapes and sizes... Whether it's leather, chrome or wood, whatever color or whatever material can be found because there are literally thousands of these on the market.
There... Thats all I have for now but i'll be sure to add some more info here soon...
It's usually very hard to find parts and accesories for your car here in the Arabian Gulf. What I do is order them from Carparts. The parts are shipped quickly, and their prices are very reasonable. Even for some of the accessories that are available here, I usually find much cheaper at carparts. Try them out!