Rufus over on WoW LJ brings up Commanding Shout, the Warrior group buff that increases maximum health of party members for two minutes within 20 yards, and comments that it doesn't work so well in solo play. Which isn't necessarily true-- there are cases when you need as much health as you can get. And he got me thinking about other buffs like that -- buffs that are really meant for group play, but that can sometimes help in solo play.
The first one that jumped to my Shaman mind is the Mana Spring Totem -- it's really meant for group play, but every once in a while I'll pull too many, need some extra mana, and drop that to pick up a little blue. Also in the Shaman's Resto tree is Earth Shield, which can be helpful in solo play, too. And while Power Word: Shield is really too mana intensive to regularly be used in solo play (it's really meant to be used in groups), there are lots of times when it's helpful with solo priests.
Usually, you should only use these things when absolutely necessary (and when you've got the resources to use them -- Commanding Shout, for example, doesn't actually give you any health, so using it in the middle of a fight doesn't help). But Blizzard has made sure we don't just have group buffs and solo buffs -- some group buffs are occasionally really useful in solo play. Can you think of any others?