The best saddle for "in your crack" climbing (we all know about those climbs, eh?) on the mtb for me has been the Titec Berserkr. I dunno if they even still make the darn thing; I bought 3 on sale last time I found them! It's a "guys" saddle, but the comfy, padded, thick nose does it for me. Not too wide to get off the back either. It weighs a bit...I use it for endurance racing (12-24 hours) with extended climbing and for other loooong rides.

On the road, I don't really sit on the nose as much, so it's not such an issue. If you do a lot of Tri's or TTs though, that could come into play.