Mega protoshield for Arduino : ID 192 : $14.95 : Adafruit Industries, Unique & fun DIY electronics and kits

Discontinued - you can grab this DIN Rail Terminal Block Adapter to Metro or Arduino Uno instead!

DIN Rail Terminal Block Adapter to Grand Central or Arduino Mega

Adafruit Proto Shield for Arduino PCB [v.5] : ID 55 : $6.00 : Adafruit Industries, Unique & fun DIY electronics and kits

ElectroCookie Proto Shield Kit Compatible with Arduino Mega R3, Stackable DIY Expansion Prototype PCB (2 Pack) : Electronics

Mega protoshield for Arduino : ID 192 : $14.95 : Adafruit Industries, Unique & fun DIY electronics and kits

It works with UNO, Mega, Leonardo, NG, Diecimila, Duemilanove, and compatible Arduinos. Yun's and Arduino Ethernets have a chunky Ethernet jack that gets in the way of stacking, you can use the stacking headers included and it will work, just doesn't sit nice and flat.

Adafruit Proto Shield for Arduino Unassembled Kit - Stackable ADA2077

Discontinued - you can grab Adafruit Grand Central M4 Express featuring the SAMD51 instead!

Arduino Mega 2560 R3 (Atmega2560 - assembled)

Are you ready? Really ready? Cause here comes the Adafruit Grand Central featuring the Microchip ATSAMD51. This dev board is so big, it's not named after a Metro train, it's a whole freakin' station! This board is like a freight train, with its 120MHz Cortex M4 with floating point support. Your code will zig and zag and zoom, and with a bunch of extra peripherals for support, this will for sure be your favorite new chipset.

Adafruit Grand Central M4 Express Featuring SAMD51 ADA4084

Arduino, Shields Products Category on Adafruit Industries

Adafruit Grand Central M4 Express featuring SAMD51 [Without Headers] : ID 4084 : $29.95 : Adafruit Industries, Unique & fun DIY electronics and kits

Here's a great way to use and adapt a world of projects and example code - the Adafruit METRO. It's a derivative of the Arduino UNO board (RS 769-7409) and it runs so the ATmega328P at 16 MHz with 32 KB of flash and 2 KB of RAM. So it's just the thing for those simple projects. Featuring 19 GPIO pins including analogue inputs, hardware UART, SPI and I²C, timers and PWM, the METRO's logic level is 5 V (though you'll find it easy enough to convert this to 3.3 V).

Adafruit Metro 328 - Arduino Compatible - with Headers ADA2488

Mega Prototyping Shield for Arduino Mega Due - DFRobot

Replacing the headers on a Mega. Can it be done? - Project Guidance - Arduino Forum

Adafruit Proto Shield for Arduino Unassembled Kit - Stackable [Version R3] : ID 2077 : $9.95 : Adafruit Industries, Unique & fun DIY electronics and kits