I also use several lower tier Pokemon on many teams that I make. Claydol, for one, is I believe the only Pokemon in the game (aside from its pre-evolution Baltoy) to not be hit by the EdgeQuake combo for at least neutral damage. On top of that, it resists Fighting as well, making it a fairly good stop to Terrakion, at least for a time. It also learns both Stealth Rock and Rapid Spin with more special bulk to differentiate it from Forretress and Donphan, the other main Pokemon with that combination. It can also use Ice Beam and do some pretty good damage against the many weaknesses to Ice.
Another lower tier Pokemon I use is Darmanitan. For anyone who's seen it in action, this shouldn't need much explanation. Scarfed Jolly 252 atk Darmanitan's Flare Blitz is just about a guaranteed 2HKO on 112/0 Modest Rotom-W, a possible 2HKO on 252/252 Impish Donphan, and a guaranteed 1-2HKO on anything else that doesn't resist it. Oh that's right, I was forgetting to include Sun and any hazards, status conditions, or any other means of previous damage.
I'm also a fan of using the severely underrated Swampert (what is it with me and non-OU Water-Grounds, I used to use Gastrodon all the time in DPPt and now that that's OU and Swampy isn't I use Swampy instead). Its capable of setting up Stealth Rocks, something Gastrodon cannot do, as well as hitting harder on the physical side of the spectrum, which is very useful against many enemies that it would be tanking such as Tyranitar and Volcarona. Roar is also a move that Swampert has access to which other bulky waters to not that allows it to stall threats, stop set-up sweepers, and, with a bit of luck (but who am I to wish for that) deal some good damage to any Rock-weak Pokemon on the opponent's team.
Those are the UU Pokemon I use most often in OU, but I do have a few teams or two with Roserade, Aakeosu Archeops, Sableye, and more.