Adafruit GPIO Reference Card for Raspberry Pi B+/Pi 2/Pi 3 makes connecting wires to the Raspberry Pi GPIO easy with no soldering required. This reference board can be used to see if the wires are connected correctly. The pins are grouped into categories like I2C, IO, UART, SPI, and power. The card is only 0.8mm thick and slides right onto the 2x20 GPIO header. Jumper wires plug right in with female sockets on top. This version works with the Raspberry Pi Model B+ / Pi 2 / Pi 3.
The Adafruit GPIO Reference Card does not work with the Raspberry Pi Model B. For the Raspberry Pi Model B, use the 2262 GPIO Reference Card for Raspberry Pi Model B.