I have been using a Williams Optics bino viewer for a while now ( thanks Meru!) in my 150mm f8 frac. The WO comes with a pair of 20mm 66* eyepieces that are really good. I'll soon be getting a Siebert diagonal which will allow me to use the bino's without the 1.6X corrector.
In mono mode I have the ES's in my signature a GSO 15mm Superview plus a few GSO plossls 32 25 20 and 15mm. Eye relief is not important in mono mode and hope the same applies for stereo viewing...is that right? I Could double a couple of the ones I have, or maybe Astro Tech Paradagims?
Recommendations...? After longer and shorter FL to go with the supplied 20mm's.
Matt