I get asked the question "which laptop should I buy?" more and more often. I'm not a particular expert with laptops, but since I seem to be more of an expert than those who ask, I'll give some background which is relevant today, and I'll write it down here so it's available for others as well. This is more like general advice, not a recommendation for any particular machine.
There are awfully many different laptop models to choose from, and most of them are OK for most users. What you need to consider is how you will use the laptop, what you want to do with it. Two main questions:
1) will you be very mobile, travelling with the computer, or will it mostly sit on your desk?
2) are you going to play games?
I'm not discussing Macintoshes. If you plan to do work, not play games, and don't require Windows for some specific application, a Mac is probably good for you, but they are not cheap. They are probably worth the price, if you can afford it, but not cheap. However, before you buy one, please remember that you risk becoming a preacher who is a nuissance to his/her friends, because preachers want to convert everyone else to their faith.
Now, to Wintel laptops - Dell, Acer, HP machines that come with Windows, and which some people (like me) run on Linux.
If you are going to be on the move with your computer, consider getting a sturdy laptop for good mobility. Not all laptops are suitable for this. The really big ones with 17" screen are simply too large to carry around. With smaller ones, e.g. the recent (as of early 2010) Acer low-end series don't have a very rigid body so they break easily.
For extreme mobility, look at the mini-laptops. The Asus Eee range is actually quite good. But only for extreme mobility. The small screen and keyboard are really a pain for regular use. You'll hate actually working on it if you don't benefit from the light weight and small form factor. The mini-laptops usually have Intel Atom and 1Gb RAM, so they are rather under-powered.
For (3-D) games, you need a good display adapter, plus fast CPU (dual-core). That takes you to a specific category and price range. I can't help you there, but you wouldn't listen to me anyway.
For any other use - word processing, browsing the net at home, writing and receiving e-mails, etc - practically any laptop is good. The CPU is not really a bottleneck. Just make sure you like the look and feel of the screen and keyboard. Those are your interface to the cyberspace, and you spend a lot of time with them, so get the kind that you really like.
Then, why are there so big price differences between laptops that have similar processing power, screen dimensions, memory, disk etc? This is because they are for different markets: home use is considered a different market from corporate use. The corporate models cost more, but there is a good reason and you might want to think about them even for home use.
The problem with many laptops (and Dell Inspiron series comes to mind in particular) is that you have a similar-looking laptop which is different. Components are changed during manufacturing, and there are multiple revisions. The laptop may have the same model number, but it has a different Ethernet interface circuit, different WLAN, different Bluetooth, possibly even different display hardware. And this means different software drivers for operating system, and that means different bugs and behaviour.
Saying someone has "Dell Inspiron" does not really tell very much. There are an awful lot of different Inspirons around, some of them stable, some not. So some people have very good experiences, some have very bad.
This is pretty okay for a home machine, except that some machines are more stable than others. But if someone is trying to maintain a number of computers and keep them with similar software configuration - a regular requirement in corporate environment - this is a nightmare.
That is why the so-called business laptops are somewhat more expensive: there the manufacturer commits to keep the model the same (or at least less different) over the manufacturing period. The same design is being made and sold for a number of months, even years, and the same OS & driver package works (mostly) in them. I believe that is why I have had such lovely experiences with IBM T43 and Lenovo T61. They're not entirely without manufacturing-time evolution, but the changes are small when compared to the fast-changing home machines.
This is also why the business laptops and their software packages are more thoroughly tested, and that shows up in reliability. If your performance requirements are not very tight (e.g. no game-play), you might want to sacrifice some of the top-notch performance for reliability, i.e. get a so-called business laptop with lower-end CPU (but enough memory!) even if something else is faster and newer. And do take a look at the ergonomy (screen in particular).
If you look at Dell, consider the business Latitude line instead of home Inspiron. Also, there is the new Vostro product line but not in Finland yet. Personally, I've liked the IBM/Lenovo ThinkPads, they have been extremely reliable (with the exception of T42 that went away quickly). Not many people have Sony machines because of the high prices, but I have a good quality image of them. HP Compaq is nothing exotic but works fine.
So, off you go, see the one you plan to buy and make sure you like the ergonomy it offers.