I suppose an Roland TR-808 drum machine would be the obvious start... While
the 808 is a classic part of the electro sound, it was never the be-all end-
all of electro rhythm machines, people used to used the Oberhimiem DMX,
Sequential Circuits TOM (and an earlier one more like the DMX which name I
can't remember now), many analog percussions synths (lots of people made there
own sounds) and even modulars (especially in the european proto-electro
productions - Krafwerk and Geogio Moroder for the best examples)
Other than that, just about any analog or even digital synth can be used
efectively for electro, but here are some of my favorites.... the Arp Odyssey
(the freakiest basslines!) SH-101, Korg Mono Poly (excellent for blippy
kraftwerkesque kind of melodic percussive sounds) Sequential Circuts Pro-One.
As for new gear to do electro with, a decent all-in-one synth would be a Nord
Lead or Nord Lead 2. It pretty much emulates (and more than emulates, it's a
great synth) just about any analog "electro" cliche sound effectively, and
even the preset drum sounds (which you can edit of course) are old school
electronic style.
-John