The Raspberry Pi mini computer is a great platform for a wide range of projects and an excellent place to start with Linux. There are other mini computers available, but few have the level of popularity of the Raspberry Pi. More people using a platform means a larger community to interact with and get help from. It may not seem like a big deal, but it definitely is nice to be able to search for the answer to your problem and find it quickly, which is what a large community provides.
Tips for Getting Started
What you need to get started at the most basic level: A Raspberry Pi, memory card, HDMI cable, USB power supply with Micro B USB cable and something to display video via HDMI like a tv or monitor. Make sure to get a power supply that puts out at least 5v and 1A. Getting a case and having a USB WiFi dongle may be useful, but not necessary to run the Pi. A computer and SD card reader/writer are also needed to write the operating system to the Raspberry Pi’s SD card.
There are a lot of kits out there and some are good deals, while others are not a good value. Do comparison shopping.
For the Raspberry Pi 1 in Models A and B you need a regular SD card, or a MicroSD card with an SD adapter. For the B+ model and the Pi 2 Model B you need a MicroSD card. It is important to buy a fast SD/Micro SD card. There are a lot of class 10 cards out there that are slow as dirt. When you are looking at SD/MicroSD card speed, look for something that lists the MB/s for read and write. 30+ MB/s should make the Raspberry Pi run well. Slow memory cards can make a Raspberry Pi sluggish.
Where to Buy
In the U.S. the Raspberry Pi can be purchased at a number of different retailers. Do not pay more than $35 + shipping for a Raspberry Pi 2. The Raspberry Pi 1 A, B and B+ should all be less than $30. If you have a Microcenter near you they often have them on sale for less than most places. Pretty much any accessory (USB device, etc) that says it is Linux compatible will generally work with the Raspberry Pi. In the next section there is a link to a list of compatible hardware by category.
https://www.raspberrypi.org/products/ – Distributors listed by the Raspberry Pi Foundation