For Socket 370: Intel Celeron 500 with 66 MHz bus speed.
This processor (codenames Covington and Mendocino) for Slot 1/ Socket 370 was popular for overclocking using a motherboard fitted with a 440BX chipset (FSB from 66 MHz to 100 MHz). Here's a curious fact: Intel produced a Celeron 300A using 0.18-micron technology with thermal dissipation of just 19 W. The Covington had no L2 cache and ran at 266 MHz or 300 MHz. Intel stopped production of this wishy-washy processor after a short time.
For Socket 370: Intel Celeron 500 with 66 MHz bus speed.
Last evolutionary stage: Celeron 533 for 66 MHz system bus.