I've been getting up at 6 am almost everyday the past 3 years and still cannot wake up w/o an alarm. Occasionally I will wake up just before my alarm goes off. Funny thing is, before I never had a problem waking up at a set time. In hs I could get up at 7 everyday w/o any alarm. I'm not really getting any less sleep (about 7 hours) so I don't know what's going on. When I was on quarter break I was getting up at 7 to goto work and it made all the difference in the world. I'm just not a 6am person.
Anyhow, I have this bells and whistles model Sony job that I use. I don't even have the radio turned on too loud but it does the trick. Has two seperate alarms and the buzzer gets louder if you don't hit the snooze and is very annoying. The geek in me liked it b/c it sets itself to the atomic standard.