It really depends on whether you (A) have the time to do it properly yourself, (B) are feeling lazy or not.

You will be able to do a pretty decent job yourself with a few simple bits & bobs. For the outside of the car you would ideally have:

1) Shampoo (I use a wax free shampoo).
2) A clay bar kit.
3) Polish.
4) wax.
5) Sponge, chamis & polishing cloth.
6) You can also use a 'quick detailer' spray to keep the car looking in tip top condition every week or so.
7) Wheel cleaner & brush. Some tire shine.

All of the above would probably cost you slightly less than the valet (Plus about 4 hours of your time), but you will be able to 'valet' your car again yourself once it starts to get dirty - & you will be suprised how quickly you'll notice it getting dirty.

If you go for the professional valet route, I would advise you to get some Ultimat Quik Detailer for keeping the car looking it's best - 20 minutes with this spray & a polishing cloth will have your car looking like it's just been waxed again.

Have a look here: Detailing World, there's lots of useful information there about techniques & products.

It's not difficult to do yourself, here is the result on my car, it took about 4 hours & a lot of elbow grease, but you can see the difference - on the plus side I now have all the products & equipment I need & can 'valet' the car any time I like a lot cheaper than paying a pro.

Before:


After just 1 clay, polish & wax:


TSC.