For the garage I use a simple reed switch. The kind that they use on alarm systems to see if a window is opened or closed. Dead simple and $4 at your local hardware store. See link below. It lets you know that it's in a closed date or not closed state (which is different from opened, it could be partially opened).
I use a light sensor to tell if the lights are on. It only works at night, but that's part of the logic I set up.
I use Plivo for the SMS service. It's a pay service, but security is great and it's super cheap. I put in $20 to start the account and 6 months later of multiple SMS messages per day I'm still at $19 and change.
I love the web page component. Very cool. Much prettier than anything I could build.
I built one using SMS. So I get a text when the door opens, and I can ask the door if it is open or closed, and open or close the door via SMS. Not as pretty as the webpage, but I like the proactive messaging. I also have it set to tell me if the door is open more than 30 mins or after 10pm. And I added a light sensor to tell me if the lights were on more than 30 mins (kids leave door open and light on frequently).
Link to light sensor:
http://www.ebay.com/itm/Arduino-I2C-Digital-Light-sunlight-intensity-lux-Sensor-Module-BH1750-BH1750FVI-/121039391267?pt=LH_DefaultDomain_0&hash=item1c2e828a23