Moaning sounds.

"Who can it be now?" by Men At Work

I just have a dull normal ringtone but my SMS alert is the Battle Celebration music from FF7.

I have "Berlin" by Alex Wurman from the Confessions of a Dangerous Mind soundtrack. A seriously rocking tune from a pretty awesome obscure movie. Because movie geeks are the best kind of geeks, you know.

I have a few that I use:

-White and Nerdy by Weird Al
-The Doctor Who theme (my message alert is the TARDIS sound)
-Basketcase by Green Day. I use it as my sister's ringer I.D., but only the first part "do you have the time to listen to me whine"

and what is probably my geekiest ringtone...

-A recording of me, in a monotone voice saying "Ring. Ring. Riiiiiing."

The Fragrance of Dark Coffee. The theme of guess who from Phoenix Wright Trials and Tribulations.

Click to have your ear canals made love to.

Seven Seas of Rhye by Queen
and my message tone
Paranoid Android by Radiohead

Sparta remix.

Mine is PARTY HARD!!! - Andrew W.K. It's awesome to have my mobile say: "When it's time to party, we will party hard!", every time someone calls me.

If you want cool ring tones for a monophonic Nokia mobile, I can recommend this site:
arcadetones.emuunlim.com

At the moment my ringtone is L's theme from death note
and my message alert tone is the fanfare from FFVII

oh yea, I forgot. my ringtone for people that I don't like is just a recording of silence

My ringtones are nerdy in other respects, mostly because I couldn't find any really good ones...

General: "Phantom of the Opera"
Dad: "Back in Black"
Mom: "Summertime" (she's a Country fan)
Little Brother: "Nothing's Gonna Harm You" (from Sweeney Todd)
Exes: "If I Only Had a Brain" (I always giggle at this one)
Texts: "The Tale of Sir Robin" (from Monty Python)
Alarm: Super Mario Bros. Theme Song

For the longest time, my text sound was Katamari Damacy but my dad started getting really mad at me whenever he heard it, lol.

The Codec from MGS.

other than that I would love to have. Rick Astley's - Never gonna give you up.

James Bond Theme.

i have "no phone" by cake. xD which is kinda contradictory i guess. i had the konami code at one point. :B

I used to have a Mario medley, now it's Bomfunk MC's - Freestyler

Clearly, the Final Fantasy medleys aren't as individual as most posters thought they were!
Myself? As a huge fan of Hideki Naganuma I have "Ska Cha Cha" from Sonic Rush as my ringtone, as well as that sound effect when you load a Metroid save game as my text tone.

I like to think Ween is fairly high brow geeky. I have 'La Cucaracha' as my ringtone.

I used to be an old skool fan of the Poke Rap,, that was killer back in Uni, these days im starting to calm down with a bit of 'Every one had AIDS' from Team America

Additionally Ive Settled on 'Whats up with it Vanilla Face' from Borat as my txt tone

black sabbath iron man, where they go:" I AM Ironman!"

For my message alert I've got the "what the fuck BOOM!" effect from Ventrilo Harassment. If you don't know which effect that is, the shortened version is at http://www.youtube.com/watch?v=QwKgIjOiKVc
Funny, yet a bit awkward when it goes off in public.
I try to make up for it with "Sweet Child of Mine" as a ringtone.

I used to have the Imperial March in high school. I'd always play it when a relatively laid-back teacher walked into the room. Once I went to college, I upgraded to the FFVII victory fanfare. Unfortunately, I had to change ringtones once I "upgraded", because my new phone doesn't support texted ringtones. Therefore, my current ringtone is "Call Me" by Blondie.

For general use, I use the FFIV airship theme.

Other ringtones assigned to specific people are:

DW1: Town Theme
FFIV: Boss Battle
FFIV: Chocobo Theme
FFVI: Decisive Battle (Boss Theme)
Lufia: Memories of the Last War
Megaman: Main Theme
Zelda: Main Theme (Carribean Mix)

My text message alert tone is the Zelda secret sound.

"Bad Religion - I Love My Computer" as my ringtone.

Most people don't get it tho.

A friend of mine might still have the Pokemon Centre tune, from the Game Boy Colour Pokemons, on her phone. Sadly mines too old to house anything more exciting than being able play Skipping Stones.

ahh, CNC's Act On Instinct =)

The DAAAAAHHHHHHH!!!! from the rabbids of Rayman Raving Rabbids. I mean come on how can you not have that ringtone. It's just so awesome having a random scream come out of no where when someone calls you and have everyone in the room staring at you as you pick up the phone.

Also my text message ring tone is the rabbid version of Beethoven's Ode to Joy.

Bloody Tears

A cookie for everyone who immediately knows the tune from the name.

Mines about as nerdy as it gets, the music from pheonix wright: ace attourney when you discover the truth at the end of a case, that "duh-duh-dudaduh-duh-duh-dudu-duh-duh.duh.duh-duh.duh.duh.duh-dudu-duh-duh-duh"

...i think thats how it goes.

though i have my phone do the bioshock circus of values clown line when i get a message, you can get all the bioshock ones off major nelsons blog.

ask a ninja song

Doom level 1.mp3

you remember the epic tune from the first level of the first doom? its that, but with real guitars and stuff. I think i got it off some mod forever ago.

My ringtone is actually the portal theme song, it cracks me up.

Lvl 64 Klutz:
Bloody Tears

A cookie for everyone who immediately knows the tune from the name.

Castlevania 2: Simon's Quest, daytime theme.

Lukeje:
I don't know whether it's actually geeky (probably more pretentious), but mine's 'Gran Vals' by Fransisco Tarrega (on classical guitar). A prize if you get the 'joke'.

Also more recently known as the Nokia Theme?