Our least used is Alchemy
Maybe the groups I've played in are strange, but we never use the alchemy skill in any of them (4 different ones so far). This may be a function of the DM or the environment. Instead of using it to ID potions, we tend to get those identified by NPC's, or in many cases, it's obvious what they are (same color, odor, and so forth as previously found ones). This saves the party having to lug around a chemistry set (alchemist's toolkit). And with potions and other chemical stuff (alchemists fire, thunderstones, etc) so relatively cheap, nobody bothers trying to create them either.
I've played in a campaign with 2 rogues, and innuendo was seldom used their either. I've yet to see profession used, though often an appropriate one could have helped (boating especially). And finally, read lips just never seems to get used. With listen checks in the 30+ zone, it seems that there's seldom anything that isn't heard that needs to be.