X10 is a costy professional switching system, with quite limited capabilities (no automatic cat feeders or a cat cam for example).
So you might consider playing with Arduino
This is a small stand-alone "computer" that can be programmed with ease over USB. The nice thing is that Arduino does not use much power compared to running a full PC. It is so small, you can hide it wherever you like.
From the basic Arduino, you can add several shields to switch appliances.
There is a relay shield for 110/220V switching
You can make Power-Mosfet shields for high frequency 110/220V switching
You can add an XBee shield for wireless control of other XBee switches.
There is a big bunch of input shields to read RFID, measure temperature, measure light, sample sound etc.
Pricing is great. Arduino costs around 20$, most shields do a similar price, and if you can solder you can cut on costs even further.
A good source for arduino projects is:
They have a nice store too:
Good books on the subject are "Making things talk" and "Getting started with Arduino"
If you buy the Arduino starter kit, you have a great set of components to start with automation, and the nice book "Making things talk" is included as well.