Almost anything made by 3dfx or Roland is very popular. Some of the best stuff, regardless of company for vintage computer gaming enthusiasts include :
Voodoo 2 12MB (x2 for SLI, especially the Quantum 3D Obsidian X-24)
Voodoo 5 5500 (any version)
Roland MPU-401 (any)
Am5x86 and Cyrix 5x86
Unlocked Pentium IIs, IIIs and above
Pentium III-S 1.4GHz Tualatin
Good PCI 486 Motherboards
Roland LAPC-I, SCC-1, SCB-55, MT-32, CM-32L, CM-500, CM-300, SC-55, SC-55mkII, SC-88
Sound Blaster 2.0 w/CMS chip upgrade
Adlib Gold, especially with the Surroundsound module
Gravis Ultrasound (any, especially the PnP)
Tseng ET4000-6100
Virtually anything made by Canopus
Ensoniq Soundscapes (except the PCI stuff)
Yamaha DB50XG and equivalents
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