This is a list of synthesizers and samples that were commonly used in happy hardcore in the 2000s. If I'm missing something and you know about it, please reach out and I'll add it to the list! I have not added verifiable sources to every item on this page yet but will make an effort to do so in the future. My sources for this are mostly people who were active producers back in the day, and videos made at the time.

Synths

Korg M1

Originally a hardware rompler. Source of THE rave piano sound. Now available as a software plugin!

Massive

Came about later in the 2000s. Used for basses and electro sounds. Still available and actively updated!
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Nexus

A powerful rompler, used extensively for pianos, pads, leads and stuff in the late 2000s. Still available and actively updated!
Sources:

Sylenth1

Used as a general purpose synthesizer, but especially supersaws. Still available and actively updated!
Sources:

V-Station

Used as a general purpose synthesizer. Saw a brief re-release in 2020 before being discontinued a second time.

Vanguard

Used for Leads, trance gate sounds, pads in the early 2000s. Still available and actively updated!

Virus TI

Hardware synth that was used as a general purpose synthesizer. Discontinued, but there is an unofficial emulator available.
Sources:

Z3ta+

Used as a general purpose synthesizer. Unfortunately discontinued and no longer available.

Samples

Vengenace Essential Clubsounds Vol. 1-3

Extensively used in hardcore to the point that individual samples like "VEC2 Bassdrums Hard 185" are a meme. No longer available for sale but still available to download if you know where to look.

Zero-G Datafile

Extensively used in hardcore, especially the vocal samples. Distributed via CD originally, available for download if you know where to look.

VIPZONE vocal samples

commonly used vocal samples. Especially the Kate Lesing ones. Some packs have been discontinued.

Classic Breakbeats

Even if you don't know them by name you have heard them.

Rave Stabs

Used in lots of songs, especially the ones more reminiscent of 90s happy hardcore. Not really from a single source but compiled from all over.

Effects

DBlue Glitch

Used in the later 2000s to make glitchy effects, often on vocals or percussion. You'll know it when you hear it. Still available and actively updated!

Other Software

T-RackS

Mastering suite that was commonly used back in the day. Still available and actively updated!
Sources: