ATmega 328P SMD version
This: https://www.sparkfun.com/products/9825 plus AVRdude will do the trick.  Just make sure to design in the 2x3 ICSP header just like on the Arudino board.  There are also ways to load both the bootloader and firmware at the same time, such as using a utility called srec_cat to combine the hex files.  

To write your user code, you can either use the ICSP cable directly and forget the bootloader, or you can design in a serial port or USB to serial converter (I highly recommend the FTDI chips, the driver support is excellent).  I would recommend designing in a serial port anyway for debugging.  It's also possible to bring out a TTL serial port on a set of pin headers and then use something like this: https://www.sparkfun.com/products/9716 .

And you will only get board area savings with the smaller chip, the power consumption will be identical.  However, there are software techniques you can use to reduce power consumption, such as putting the chip into deep sleep and then waking it back up with the watchdog timer.  The watchdog timer has a dedicated RC oscillator, so you can turn of the core, the main oscillator, and all of the peripherals and just wait for the watchdog interrupt.