I acquired a 'new-to-me' Leigh D4 awhile back and have only used it a couple of times with an old Craftsman fixed base router I've had since about 1970. But now it started arcin' an' sparkin'. So I think it's time to finally spend my 'Economical Stimulus Check' that hasn't yet been touched!
The D4 manual suggests having two fixed base routers.
My present router arsenal is a PC 7539 in a table, a Makita 3612 plunge router for general use and a Bosch Colt for edge routing, setting in hinges, etc.
I have often wished for a horizontal router table, and I am thinking this might be an ideal use for the Makita with an external speed control. I would be wary of using the Makita in the D4 because if the plunge lock slipped, it might make 'router dust' out of the D4.
That leaves me with a clean slate for the D4 and general use. On a quick swing through the Borg tool section I saw several dual based router offerings -- Ridgid, Hitachi, DeWalt, Porter Cable, Bosch, etc in the $200 range that might fill the bill. Sears has a couple of these in the $120 range. Of the bunch, the only features that stood out superficially was the PC had a collet separate from the motor shaft and the Hitachi had a garish green/fake chrome finish that reminds me of the latest trend in athletic shoes and Asian automobiles.
I'm sure there are other options too, e.g., Sears has a smaller fixed base that looks quite nice for $85. PC has one for $150 at the Borg. I could dedicate a couple of these for the D4 and go with a third one dual-based.
There is also the recommendation that 8mm shank bits be used with the D4. My D4 has a couple of 8mm bits with it that I haven't used. It would be nice if whatever router I settled on had available an 8mm collet, rather than an 8mm insert to be used in a 1/2 inch collet.
I'm entirely open minded on this. With all the options, mutations, and permutations I expect several here have been through this already. While there may not be a consensus, there must be some solid advice that will point my nose in the right direction!