I've been lucky to run across a fair number of undescribed species, many of which I didn't realize were undescribed until after the fact. A couple I have seen I knew were something new, but held of on collecting either because of permit issues or the fact that I wasn't entirely sure that I had the know how to describe the species myself.
Here are two I didn't realize were new when I saw them, just assumed it was a lapse in my knowledge. However after the fact I have been contacted by Ecuadorian herpetologists who believe that these represent new species.
Unidentified Atractus by
Anton, on Flickr
Wet Saphenophis by
Anton, on Flickr
I don't have the photo uploaded to a photo sharing site but I also found a species of Pristimantis in the area, that I knew was something new and different, I photographed it and released it where found. About a year later it was described as Pristimantis buenaventura. Not too tough to find new species in the area as there is a lot of surveying left to do.
This one here from Borneo, may or may not be undescribed, not entirely sure.
Mystery Frog by
Anton, on Flickr
Its a Philautus sp. closely related to bunnitus & kerangae. When I contacted herpetologists working in Borneo about it I was told it was indeed a bit of a mystery and that a similar one had been collected recently nearby and genetic work was being done to see if it was indeed a new species or not. Don't know what the result of that was.
I recently found a semi arboreal toad (Rhinella sp.) in a fairly remote portion of Peru, I knew right away it was something special. I really struggled with the idea of collecting it for a species description but in the end left it well and happily hopping away. As it turns out someone is already working on describing it.
There is lots to find out there still!