I am buying a new desktop PC in early 2013, anyway this question should apply to someone intending to buy a new laptop/ultrabook as well.
This machine is not meant for gaming, and if I ocasionally do it, I can survive with minimum graphics. However I may need some heavy multimedia edition or multitasking at times, so basically my greatest priority is a good processor, after that perhaps average graphic card (if onboards are not enough, I am still not informed enough about that), at least 4GB of RAM with possibility of expansion.
I know there are some PC models specially designed to ship with Ubuntu, which is the OS I use the most these days. However, most people around me use Windows and some software with unsupported versions for Linux and not having a Windows license becomes a bit problematic.
Given that, I would like to find information about which PC models or even manufacters currently on the market have the best compatibility with Ubuntu, I am still undecided between building my own desktop or buying a pre-made model, so I would like to find information both for certified models and certified hardware or even Ubuntu partners that may work closely with Canonical.
Where to find this information in order to make sure that I will have a good experience with Ubuntu on my new PC in the years to come?
See the Ubuntu Certification website at:
http://www.ubuntu.com/certification/
Specifically, for desktops and laptops/netbooks, go directly to:
http://www.ubuntu.com/certification/desktop/
The best way to tell if hardware is working in Ubuntu is to check the official page:
Ubuntu Desktop certified hardware
My thoughts about how much of a "guarantee" this database of hardware gives you in practice:
Some manufacturers (OEMs) silently use other hardware components with similar specifications. "300 Mbps Wireless LAN" in the specifications is subject to change on their side and they're free to supply Canonical a Linux-compatible one and another (cheaper) one to you.
Here's a nice example of that: LP Question "Feedback on the Dell Inspiron 1545" in Ubuntu Certification Programme where Dell silently changed the Bluetooth module with a totally different one, breaking the certification programme.
My conclusion: OEMs take (too much) freedom in their choice for components and there's no way to tell the exact configuration in terms of vendor/product id's of the components you'll get after ordering. Take this Certification list not too serious, but it will give you a rough idea.
I would also suggest that you first look for minimum hardware requirements of your Ubuntu version here. Also Ubuntu website has a list of certified devices as mentioned in izx's answer.Make sure you confirm the specifications of the device from hardware provider's home page.
You can check here for desktop and laptop compatibility that has been tested by Canonical: http://www.ubuntu.com/certification/desktop/
or just buy one of the great machines from System76: http://www.system76.com
Then again, I'm running a five-year-old HP EliteBook 6930p, and it runs like a champ.
My experience with Ubuntu (since 8.04) is that if you don't have brand new components in your computer it will work. For example my laptop an Asus 1201n brand new when I installed 10.04 it had a problem with the wireless network, it was a easy fix after you Googled your hardware and a year later with a fresh 11.04 everything worked just fine.
But this is just my experience, I think you should find a computer you want and then Google it to see how good it's supported. But don't forget what gertvdijk said, you should know the exact model of the components in your computer, like CPU, graphics, network card, etc.
This question can't be answered with a good fact since the support is constantly extended and any list of hardware support will always be a step behind.
As I said, look around, find a computer you want and then look around to see how well the support for that computer and the components in it are.
good luck!