Is there a song that you just can't stop listening to at the moment?
And you never get bored of, no matter how many times you listen to it?
And when you're not listening to it, you're singing it/humming the tune to it?
And when you're not singing it/humming the tune to it, you're telling anyone who will listen about how awesome it is, until they start yelling at you to shut up?
And most importantly, you have no idea why you are doing any of these things?

Okay, I'll stop rambling on about nonsense now!

I have a few songs at the moment that I am obsessed with for some random reason.
They are:

Muse - Plug In Baby (I have Guitar Hero 5 and this is one of the songs on it. I keep on playing it over and over again!)
My Chemical Romance - Honey This Mirror Isn't Big Enough For The Two Of Us (MCR, could you please make the titles of your songs a little bit shorter in the future?!)
My Chemical Romance - Our Lady Of Sorrows

Well, over to you now!

i tend to have phases more than one set obsession on a song. one week it may be this, another, that. it changes, but when it hits, i do listen to whichever gets caught in my head over and over and over and over until it goes away. xD
ignoring it never does the trick.

The Poet and te Pendulum by Nightwish and Somewhere by Within Teptation =D

I've never gotten as bad as the fourth question. But if there have been two songs in the last couple years or so that embody the first three questions, those would be

Finger Eleven - Paralyzer

and

Social Code - Satisfied

So can not wait until the end of March when Social Code's album drops in the US. I work within walking distance of the most shopped mall here in VA Beach and every time a work project ends I nip over there to poke around and maybe buy some stuff. After the March project's over, I'm making a beeline for the FYE there so I can get that album.

Two songs that I listened to incessantly

Might Tell You Tonight - Scissor Sisters

and

Northern Sky - Nick Drake

Right now I have one. It's been my favorite for about a year.

Survive- Rise Against

I KNOW their titles are long! But all of their music is soooo good!! Have you see Our Lady of Sorrows live (Drunk Version)? It owns.

These songs are stuck in my head:
Forever and Always
Already Gone
Bad Romance (Curses!)
Christmas Cash (Shane Dawson version, "I want A**)

Love Drunk by Boys Like Girls. Thank God it's an awesome song !!!

Telephone (Lady Gaga feat. Beyonce) - LOVE THAT SONG!

Bad Romance (Gaga) - That weird, freaky demon chant she does "Rah rah...". I can never get it out of my head.

Tik Tok (Ke$ha) - So catchy!

Well... I've been incessantly listening to these songs... I know all the words. I'm just too cool for this :]
It's The Way You Make Me Feel, by Steps
Seasons of Love, from the musical, Rent
and... my personal favourite:
What's My Name?, by Naboo (it's a song from The Mighty Boosh's Future Sailors tour... if you saw it, you'd understand.)

That's one for me. I normally don't listen to top 40 songs but Lady Gaga is one of my guilty pleasures.

Just lose it - eminem.

and

The Real Slim Shady - Eminem.

From the moment I saw the teaser for So Much More by Bentley Jones I was hooked instantly. I couldn't wait for it to be released and I love it! Alpha Dog is another one of his songs that I like. I never get tired of any of Yellowcard's songs either.

I also can't Margeret's boss theme from No More Heroes Desperate Struggle out of my head! So weird, yet so catchy. "Margaret is greek, you geek. It means 'a pearl', I'm a good girl. Boys can not crack this oyster shell, so go on. Look around! It's quite like you're the best; it's a such a bore. Another hero! Oh please!"

Vanilla by Gackt fits question 1, 2 & 3.
Such a naughty, naughty song. XD And I couldn't concentrate all day after watching the PV. Seriously.
I just stared into space like "Hee-hee-hee!" My mom was like "Earth to child! Where art thou?" Gackt is teh smex.

Now Three by Vienna Teng also invades my mind. Such a beautiful song. D: So....distant. If that makes sense.

Jinsei Bimi Raisan by Ali Project is addictive, as well. It's creepy as heck, and is made of Epicnicity. (Yes, I like making up words.)

One song I always have in my head is, "The tailor shop on Enobizaka", by Luka Megurine, a vocaloid. I really like the lyrics of the song, I can't explain it myself.

Seminole wind- John Anderson
Seven Year Ache- Roseanne Cash
or any track off the AVATAR soundtrack.

Lol. I just got over a bad case of the 'Bad Romance' (Lady Gaga) bug, but whenever I knew I was gonna rock it, I tend to isolate myself away from others by plugging in headphones. With this song I can't either stop saying 'Love, love, love!' (or whatever the heck she's saying), or the first half of the opening--the gibberish stuff (...gaga ooh la, la somethinsomething 'Romance')

And also lately I can't stop singing the friggin chorus to Nami Tamaki's 'Shining Star'... I mean it's bad enough that the J-pop song is done off the beat of 'Twinkle, Twinkle Little Star', but when you throw in one line of English between two or three verses of Japanese, it tends to get lodged right in your brain.

I can't stop listening to Automatic by Tokio Hotel.

Even though the song annoys the hell out of me, I can't get Blah Blah Blah by Ke$ha out of my head. To make it worse, I only know two lines from it. Sigh.

The Girl and If I fell by Beatles

gossip - heavy cross
lexy & K-paul - lets play
and modest mouse - 3rd planet

You know it's funny. I have sort of a Katy Perry thing going with her and this song. Like Perry, it would make my life so much easier if I could just hate her work and be done with it. But I just can't do that. She's too much fun to hate her music so easily.

Ke$ha- Dancing With Tears In My Eyes && Drake - Sooner Than Later

Boys Boys Boys by Lady Gaga + Confrontation By Otep

Paparazzi by Lady Gaga and The Midnight Beasts Tik Tok parody.

Is it okay to say "Oh No" by Marina And The Diamonds as my guilty pleasure? :P