PCX1, PCX2, M3d (PCX2 by Matrox). There might be others I'm not aware of (I don't follow ImgTec like you). And the DC was not a success in the videogame market.
I didn't follow IMGTEC until late in the Neon 250's life either. So I admit I don't know that much about the PCX1 and PCX2. But weren't they decent competitors to Voodoo1? Someone else will have to enlighten us there.
You can say that DC as a console failed yeah, but we're not talking about Sega's failures. From IMGTEC's perspective the graphics chip they provided to NEC/Sega was a massive success. They sold 13+ million in DC alone and the same chip dominated the arcade market in Naomi 1 and 2 and is still doing well to this day. PowerVR DC was anything but a failure. Kyro and Kyro II weren't failures either. We've certainly seen IMGTEC fail in the past, and to be clear I'm not saying Sony made a mistake by not using them for PS2 or anything like that. I'm just saying that to say they've failed time and time again is way over the top. IMGTEC, or more specifically PowerVR wouldn't be here today if they'd failed time and time again.