I'm currently building an alarm clock myself 
I have quite a different feature set though, hehe.
I have a 4x20 LCD display, buzzer&LED, IR receiver and wifi shield.
My thoughts were:
- I want to be able to set on a calender when it has to wake me, so I can set a week of different wake-up times without having to fear it isn't turned on or forgot to set it to the correct time for the day (say, each day your classes start at a different time).
- I don't want to reach all the way to to turn off the alarm.. A remote will fix this.
- I want to see if I have new e-mails (hey, why not??).. hence the bigger display, aswell as an extra excuse to add wifi capabilities =)
Why wifi? I don't have an ethernet cable going all the way to my bedroom.
Ok, I don't have an RTC.. instead I'll make it sync with the internet, so in effect I have that one covered.
You have me beat with the accelerometer and temperature sensor though =P