I have some baby bunnies right now with the sneezes - they were on Bactrum and now are on Baytril.  From what I've heard from other rescuers is that the sneezes without discharge is usually allergies - but if there IS discharge that it may be some type of sickness.  However, since my buns have been on TWO medicines, I am going to also check on what Tink recommended and make sure my babies are in a warmer place - because its "Big Baby" thats sneezing and now "Teeny Baby" as much - so maybe Big Baby is trying to protect Teeny and keeping her warmer? My house isn't all that chilly, but there could be a draft in the evening. 

My cat was just diagnosed w/ allergies.  He takes a kitty claritan like pill daily.  We found out it was allergies due to:  redness between the eyes and ears, loss of 2 complete claw nails, and occassional sneezes.

I understand that animals w/ shortened snouts and close noses (bunnies, guinea pigs, pugs, etc) can be prone to sneezing bouts and upper resp infections due to the shortened snout.  Hope that made sense?