Bad Maniacs by kors k as teranoid, from IIDX 17 SIRUIS. A difficult hardcore song with lyrics spoken in a feminine computer voice about killing and/or fucking you. "We are... playing to die!"
"How much do you hate me now? That is not enough. I ?????? you. We will be back to ???? again soon."
Contract by DJ Yoshitaka (aka Suzaku), also from IIDX 13 DistorteD.
20,November by the now-retired Reo "DJ Nagureo" Nagumo, from the very first beatmania title, has become one of the most iconic songs in the Bemani franchise, and November 20 has become not only Nagureo's birthday, but also a day celebrated every year by fans.
However, interestingly, according to the poll in beatmania THE FINAL website, the most popular song during 5-key era is not "20, November," but super highway by nouvo nude. This song is included in beatmania IIDX 13 DistorteD.
Genocide by DJ Killer (a previous pseudonym of Tatsh) from beatmaniaIIDX 11 Red.
Nageki no Ki by Kinjinshi (a special pseudonym of DJ TAKA) from beatmaniaIIDX 13 DistorteD. According to TAKA, the intention was to write a song to be the king of kings. It shows.
Scripted Connection=> from IIDX Happy Sky is an epic 5 1/2-minute techno track, with a very unique gimmick: the Normal version fades into the Hyper version, the Hyper version fades into the Another version, and the Another version fades in from the Hyper version—put all three versions together for the aforementioned full version.
Go Beyond!! by Ryu* vs Sota, from IIDX: Distorted Rates up there as one of the hardest songs in the game, but probably one of the most awesome songs as well.
Sense 2007 by good-cool, from IIDX GOLD. The song may suck for you, but the video's awesome.
Some video with "We can fly away" either in the lyrics or in the video, which also had the "camera" flying around the inside of some sphere
That was HORIZON on IIDX RED by LIA (actually, it's kors k with Lia singing). If you read the description at RemyWiki it explains the song and video. Some people may find the song depressing, some may find it uplifting.
She is my wife by Super Star Mitsuru, aka TAG. Notable for the hilarious background video (shown in the link) where TAG, dressed in a campy superhero outfit with large sunglasses and feathers, dances with dj TAKA, L.E.D, Ryu*, DJ Yoshitaka, and kors k in an extremely fabulous fashion.
Live version performed at AOU 2011, now with even more hilarious cardboard cutout of Ryu* holding a boom box.