Usually my husband’s radio alarm clock. Which he has set to the worst station in town (not deliberately–it was good before it changed formats, but the new one is so bad it give him and incentive not ot stay in bed, so he left it there.)
My girlfriend, during the once-a-month weekend we arrange a cross-country visit. 
My cat Hobbes is most often responsible for disturbing my sleep, which is okay when I have to work, but on weekends he needs to understand that I do not need to get up as early as I do on weekdays. As soon as it’s daylight he’s at the window, which means I tend to get less sleep in the summer. His favorite method of waking me up is to paw at the blinds.
Our alarm is a clock radio, so we wake up to the talk radio show by two guys we like. They’re pretty funny and reasonably intelligent. It usually takes me a few minutes to wake up, and I frequently dream something about whatever they’re talking about before I wake.
Baby punching me and giggling. Evil baby.
Or one of the cats doing something loud and stupid.
Two insane furballs (cats) that think those last precious moments of sleep are overkill and I don’t really need them. So they conduct high speed chases complete with tackling and rasslin’ right on the bed.
Or…
Cuervo waking up hungry and pretending to love me very much by walking around and on top of my head purring loudly and licking the top of my head.
Or…
If I’m out of town, my phone’s alarm is set to play Bach’s Fugue in D Minor.
On good days, the alarm clock, or needing to pee. On most days, dog #1 who has taken it upon himself to scratch my side of the bed to tell me it is time for breakfast, usually 20 minutes before the alarm. He’s quite devoted to my wife, usually, but somehow I’m the guy for breakfast.
Blimey some of you wake up early. 3 or 4am is still the middle of the night!
If my alarm isn’t set on my mobile then i just wake up naturally at around 8am,I dont think anything in particular wakes me up…hmm unless i need to pee.
Morning wood. Sometimes it wakes up my wife, too. 
My son. He is almost 10 months old and he likes to hit my face while I’m asleep. Of course, him and his mother have been up for about twenty minutes before this happens, so they get a kick out of it. I kind of don’t. (Then again, I kind of do.)
Brendon Small
Cats. We have cats.
12 pygmies, dressed in 18th century colonial America period attire, playing “More than a Feeling” by Boston on a series of PVC pipes, a la the Blue Man Group.
That’s weekdays, at least.
4:20… every morning… I feel the need, the need for peed.
My alarm clock will get me vertical, but I’m not really awake until I’ve had my shower, and a cup of Fast Eddie’s coffee.
One alarm clock with two alarms set half an hour apart with a cellphone alarm set to the :15 mark between the two. Alarm #1 (clock) is a La Nueva 92.5, a local salsa/merengue/Latin pop station. Alarm #2 (cellphone) is a short clip of Faye Dunaway from Mommie Dearest. Alarm #3 (clock) is beeping.
Back when I had a regular schedule, I could easily set myself to wake up at a certain time. These days (and for about the last 9 years, TBH) my work schedule varies wildly, starting between 6a and 2p and ending between 1p and 12a. So I can’t get into a pattern anymore.
My cellphone, either an alarm or someone phoning me. Failing that, I’ll wake up when I’m darn well ready.
The hamsters seem to have nibbled my entry away.
My alarm clock. If that doesn’t get me up, my wife;'s alarm. If that doesn’t do it, a hungry cat will.
When I was a kid, my mother used to wake me by dropping my cat on my face.
I’ve never owned a declawed cat.
The sound of the rooster’s crow, mamma cooking in the kitchen, and Arthur Godfrey on the radio.
This morning, it was a very mild earthquake. Normally, it’s my two year old son around 6 a.m. I can hear the grin in his voice before I even open my eyes. “Hi, Mommy.” Then he’ll tug the covers off, find my hand and try to pull me out of bed.
I just wake up whenever I need to wake up. I’m not really sure why that is, but if I need to wake up at a certain time, that’s when I wake up.