Taken from my Last.fm list:

1. The Mad Capsule Markets - W.O.R.L.D - 1072 plays
Because it's my favourite song of all time and I love it. It just sounds so perfect in my ears.

2. Souls of Mischief - 93 'til Infinity - 440
Doesn't really count because the bulk of that is from about 5 days where I just spammed it to hell, but a good song nonetheless.

3. ケツメイシ - Tomodachi - 421

I really, really love this song. The string and piano melody just makes me happy on the inside and the flow of the lyrics is really nice.

4. The Mad Capsule Markets - Kumo - 318
It's played a lot because it's a nice atmospheric chilled out song and I play it at night a lot.

5. The Mad Capsule Markets - Norumaaru Raifu - 226
Awesome bassline on this song, it makes me air bass and groove heavily.