Adafruit's pro trinket was designed with 18 GPIO, two extra analog inputs, 28 K of flash, and 2 K of RAM. Because sometimes, you just need more of everything. This board has USB bootloading support using a Micro-USB jack. We also added Optiboot support, so you can either program your pro trinket over USB or with a FTDI cable. The pro trinket PCB measures only 1.5" x 0.7" x 0.2" (without headers) but packs much of the same capability as an Arduino UNO. So it's great once you've finished up a prototype on an official Arduino UNO and want to make the project smaller.
The pro trinket 5 V uses the Atmega328P chip, which is the same core chip in the Arduino UNO, Duemilanove, or Mini at the same speed and voltage. So you'll be happy to hear that not only is the pro trinket programmable using the Arduino IDE as you already set up, but 99% of Arduino projects will work out of the box.
EVAL BOARD FOR ATMEGA328P