I recently installed a TED ( The Energy Detective) 1001 power monitoring unit and I am pretty happy with it. It shows things like your current KWH usage, to date usage, estimates your electric bill, etc. It even displays the CO2 output for your part of electrical use and logs your voltage.
An optional software package provides a cool Flash display of the data as well. The technically proficient will enjoy opening a router port and displaying the data on a web page on the internet. The REST server and XML output is nice for custom web pages and applications.
Priced at $150 to $190, it is a good value. Much better than monitors that simply count how fast your meter is spinning. The installation is simple for anyone that has replaced a circuit breaker, or a handy neighbor.