Originally posted by UserAccessDenied Only criteria: It must be a prime! There is no cost restraint; but if your suggestion is a FA* 600mm F4... Please list an additional lens that the average enthusiast can afford too!
Er, if your yearning for another lens is that indefinite, maybe just postpone your decision and go on shooting what you have, until you see a little clearer what limits your photography? To offer meaningful advice beyond that, one would need more information about your shooting and subject preferences.
If the main motivation is to collect lenses, well, get whatever your heart desires and your credit can buy. (I'm not saying this to patronize, but because I think that being clear about your motives for wanting another lens would really help you with the decision.)