The Atmega328P and nRF24l01+ combo is also a quite common thing to use over and over again in wireless sensor nodes, remote controls and so on.
I’ve chosen to make an adapter for the Arduino Pro Mini (the 3.3V version) to be able to piggyback small SMD versions of the nRF24l01+ with 1.27mm pad pitch on it. This way you have a tiny board sandwich which is not much bigger than the Pro Mini without the need of wiring everything up over and over again.

A quite uncommon soldering technique is required to connect the adapter and the pro mini: align the holes of the pads of the Pro Mini and the adapter and after heating up the top pad, let the solder reflow to the bottom pad through the top pad. Of course you can solder headers as well. There is room on the board for a 0805 capacitor (0.1µF-10µF are sometimes used to prevent power issues while transmitting). The VCC and GND as well as the optional IRQ pins of the radio are broken out on solder pads and have to be wired manually, since I didn’t want to make the adapter too big and still leave some flexibility.

Eagle files:
NRF24proMini