For smaller boards, EAGLE is pretty darn good, especially in terms of getting up and running in as little time as possible. There are many tutorials online, the most useful ones seem to be from SparkFun, starting with this:
http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=108
and tangentsoft.net:
http://tangentsoft.net/elec/movies/
Many boards' design files are available in EAGLE's format, it's very much worth learning so you can explore designs like... the Arduino Duemilanove (!):
http://arduino.cc/en/uploads/Main/arduino-duemilanove-reference-design.zip