I think you will learn some new stuff by doing it yourself. Look at the examples given above ..
Take a look at this one, which also has the schematic diagram: http://arduino-direct.com/sunshop/index.php?l=product_detail&p=155
You might decide to use optical isolation like in this one: http://arduino-direct.com/sunshop/index.php?l=product_detail&p=156
Get some prototype / perforated board and built the first one that way. Later design a PCB if you want. Get your design working first..
More about relays and power here: http://arduino-info.wikispaces.com/ArduinoPower
PM me if you want just the relays themselves, pretty cheap... I am thinking of stocking some..