I highly recommend either the MCCI /Nice SuperEISA, or the Tyan S1437. Both can accept 1MB of cache and 256MB of DRAM using sixteen 30-pin SIMMs, and are based on the SiS 411 EISA chipset. I have a small preference for the SuperEISA, as I feel that the build quality is slightly better, plus I had to do a soldering job on the Tyan board to get 1MB of cache to work with 300mil wide SRAMs. The advantage of the Tyan is that it has two VLB slots rather than the one on the SuperEISA, and it uses tag RAMs that are much easier to find, especially if you want 12ns.
The Tyan board is relatively rare. I've only seen two for sale in the last 12 years. The SuperEISA is relatively common for an EISA board, and there is currently one on eBay, though I think it costs $140. I think these days it might be difficult to get an EISA board for less than $100.
I also have some experience with EISA boards based on OPTi chipsets. These seem to work fine, but generally support less cache and memory. They're also a bit slower than the SiS chipsets. I've also seen a VIA based board floating around on eBay, but I have no idea what it's like. I believe it started life as the Symphony EISA chipset, but VIA bought out Symphony and gave it a new name. I only have one ISA board based on a Symphony chipset, and it's decent.
The Intel based EISA boards are supposedly the best ones to have if you want to run 50MHz, as they have an advanced cache design. I have no experience with these either, but they don't appear to be very common (I've never seen one for sale). They are probably also somehwat feature limited, as I believe they tend to be older. The first revisions of the chipset were also buggy.
There is one other board that is pretty good, and is also based on the SiS chipset. It's made by A.I.R. I think it's called the 486EI. This was also one of the more common ones. Unlike the other two I mentioned, this one can only accept *just* 512kb cache, but it CAN accept 256MB in 72-pin SIMMs, which are easier to get. It's also somewhat unique in being the only EISA board that can accept 3.3V CPUs (only in the final revision). Sadly, it does not support write back L1 cache.
"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium