Many links...
http://www.dansdata.com/gz104.htm

Demonstrates how one can play with robots and microcontrollers with any budget. Money is no barrier to getting into it.

I came across this site with a bunch of pre-canned recipes for bit manipulation: http://graphics.stanford.edu/~seander/bithacks.html

As a precursor to an 802.15.4 controlled watering system, and to get familiar with the development environment, I am building a clock based around a Jennic JN5139.

So far, I have a timer interrupt firing once every 16x10^6 cycles, or nominally once per second. Measuring the drift over an 8 hour period, the clock has so far lost 1 minute. I'll tweak the timer to account for this drift tonight, after I have more data.

Some ideas to implement:

In this application note, Atmel describe how to detect zero crossing on an AC waveform using a handful of passive components. This is useful for triggering triacs, as well as the home automation protocol X10.

Remember that there is no isolation between the microcontroller and mains here, so take heed to their notes regarding surge supression.