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.
HELL SCAPER by L.E.D. LIGHT-G, originally from GOTTAMIX. With high speed gabba with senseless psychedelic animations, it's a 2-minute rave!.
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.
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.
Pretty much anything Tomosuke does under his Zektbach alias applies to this.
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.
From the same composer of "Scripted Connection =>", we have ANTHEM LANDING, a six-minute Latin/eurodance track that serves as Resort Anthem's Extra Stage. Like SC=>, the track is divided up into Normal/Hyper/Another sections.
Every single Lincle Kingdom boss song. Slaughtering music game demons has never been this exciting:
S!ck by kors k (under his Eagle alias), which features vocals from "Rising in the Sun", as well as samples from other kors k songs.
SYNC-ANTHEM by Tatsh, with Kanako Hoshino on vocals. It's "ANTHEM LANDING" meets "RED ZONE" meets "Wise Up".
Kasoukuukan no Tabibitotachi, or "Travelers of Virtual Space" as displayed on the LED arcade marquee. Yep, it's another extended Tatsh song...but wait! This time, instead of Normal/Hyper/Another, the song is split between Single and Double mode. Talk about a clever trick to get people to play Double mode.
The boss of Sector A, Torikago no Houou, a collaboration between L.E.D. and Yuuhei Satellite, the latter of which is well-known for Touhou arranges.
The Spada✝leggendaria selecttheme, perfectly fitting of the fact that you're about to face one of the game's boss songs.
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. Wound up appearing in EMPRESS arcade, as a revival.