that have the power to do what i need
Power is an ambiguous term. All modern Arduinos have the same computational "power." If you want smaller, get a Mini or Pro-Mini. You'll have to add a USB-to-serial converter and/or header pins, but they are small.
Or you could just get the credit card sized Uno/Duemilanove and some variant of a Proto-Shield. That would easily match the "power" needs of your project.