1.) Rendition Verite V1000: It was the
FIRST 3D card EVER made. I still have one, and it works. I still remember good ol' V-Quake

.
2.) 3DFX Voodoo2-SLI: No intro needed. One of the best setups EVER to be created.
3.) NVIDIA Riva TNT2: Proved NVIDIA was serious about ripping the performance crown from 3DFX.
4.) NVIDIA GeForce2: Ended a great era-effectively ending 3DFX for good.
5.) ATI Radeon 9700 Pro (or just R300 in general): The first card that really proved ATI was game.
6.) NVIDIA GeForce 6-Series: After the GeForce FX's defeat at the hands of ATI, this showed that NVIDIA wasn't going to let the performance crown go
that easy.
EDIT: Correction to #1: the V1000 was the first 3D
accelerator ever made. You guys remember those good ol' S3 Virge things don't you

? Yeah, those were 3D
DECELERATORS.