If you want to play a low power Arduino Standalone you can use Atmega8L at 3.3 V power with 8 Mhz internal clock:
1 - Plug the ATMega8L micro to an Arduino board to burn bootloader.
2 - Edit burn file in bootloader folder.
Before burn bootloader you have to change burn file
change --wr_fuse_l=0xdf –wr_fuse_h=0xca
to --wr_fuse_l=0xd4 –wr_fuse_h=0xca
more information about fuse bytes in ATMega8 data sheet
AVR Fuse Calculator here http://palmavr.sourceforge.net/cgi-bin/fc.cgi
3 - Download this bootloader (for ATmega8L at 8Mhz, i.e. using internal crystal). Or compile your own one from source. Backup the original ATmegaBOOT.hex file in the arduino-000x/bootloader folder. (Rename the downloaded file to ATmegaBOOT.hex.)
4 - Burn bootloader
in linux you have to execute burn as root (type sudo burn)
Once you have burn the micro build this simple circuit and you can program it normally em
but you have to modify some files in Arduino IDE.
5 - Edit preferences.txt file
6 - Edit makefile
In arduino-0007/lib/targets/arduino edit makefile
change F_CPU = 16000000
to F_CPU = 8000000
Now you are ready to buid this circuit:
7 - Program the micro, for example use led_blink example
To program the micro you can use an Arduino board without the Atmega as a serial adapter or use a Mini USB adapter (as Arduino mini).
more info: http://www.arduino.cc/en/Guide/ArduinoMini
RX pin (Arduino board) connected to pin 2 in ATmega8L TX pin (Arduino board) connected to pin 3 in ATmega8L
Some info on how to make it run on 4Mhz (to lower energy consumption even more): http://www.cs.colorado.edu/~buechley/e-textile_kit/e-textile_kit_tech.html