Technochips

Doombook.

I don't really listen musics other than the one inside my music folder (which contains portal & doom soundtrack and that's it)

In regards to doom soundtracks, you may or may not know that many of the folks here who make music for custom maps, also share their MIDIs in mp3 format at times. In case you find a catchy tune you like, it may be interesting to see if the readme provides information as to who made the particular MIDI, so can grab it for you playlist. There is no such thing as too much music, if you ask me. :-)