Had the same issue with my iphython notebook (IPython 3.2.1) on Linux (ubuntu).
What was missing in my case was setting the master URL in the $PYSPARK_SUBMIT_ARGS environment like this (assuming you use bash):
export PYSPARK_SUBMIT_ARGS="--master spark://<host>:<port>"
e.g.
export PYSPARK_SUBMIT_ARGS="--master spark://192.168.2.40:7077"
You can put this into your .bashrc file. You get the correct URL in the log for the spark master (the location for this log is reported when you start the master with /sbin/start_master.sh).