As it says in the title, make a list or reply with what is good at performance and cost. I have been thinking of either buying Raspberry Pi or Arduino, but wanted to see if the forum could help by recommending others like the 2 that cost less and perform almost like them. I don't really plan on doing anything if I do get any at the moment, but it would help if you could leave a description or link as to what its capabilities are. Thanks for looking!
For the money the Ardunio Uno Revision 3 is hard to beat, complete, ready made, ready to run.
It has loads of ready made software along with many tutorials to get you going and an active help forum. https://arduino.cc/en/Main/ArduinoBoardUno
MBED has a good community and loads of code, but they expect you to do some work. Porting ARM CORTEX code from one version to another can be pretty straight forward. I dont know much about the other systems. The MBED tools are pretty good as well