Believe it or not, Xatu hasn't made its way onto all of my teams.
Tentacruel has. From my Red Version (which I still play) to my Smogon team, it's always there. Although it has many uses, I tend to make it a Utilitycrue, with Knock Off, Confuse Ray, Toxic, and Surf. It's oft-underestimated Sp.Def allows it to take Psychics, Earth Powers, and Thunderbolts like a champ, and its type combination gives it some useful physical resistances. All this adds up to a 'Mon that can switch into most sweepers and neutralize them by Knocking Off their Life Orb/Choice Item and inflicting confusion.
With Barrier, Toxic, and Mirror Coat, it becomes an unnaturally fast Toxistaller + wall...
You could also go the special sweeper route, and give it Sludge Bomb, Ice Beam, and Surf.
Yeah... Tentacruel FTW.