My first nerdy ringtone was Song of Storms/Windmill hut from LoZ. This was on an old ass monochrome phone, which didn't have bluetooth, memory cards or even a goddam USB cables. In fact, merely being able to play MP3 meant it was top of the line at the time. I order to get this as a ringtone, I had to find it on the internet, write down the URL of the MP3 file, then type it on the primitive thing that passed for an internet browser on it. At the time I was certain it would work but today I'm amazed it did. (It was the background song of the windmill, not the Ocarina song - skip to 0:08).
When I switched phones I actually knew about how MP3s worked so I ripped part of Bioshock's intro, more specifically Andrew's speech. It may have been my favourite ringtone ever, but I eventually got bored of it, and by eventually I mean this year when I got a smartphone and was too lazy to create a folder just for ringtones. (3:37 to about 4:47, but in practice by about 4:20 it would go to voicemail.)
For a while I wanted to use the opening or ending themes of World of Goo, but I was too lazy to edit them and they have a quiet intro during which I wouldn't know if my phone was ringing, so I didn't. Nowadays I just use Aggrieve [http://homestuck.bandcamp.com/track/aggrieve].
