You should ask Thund, he will give you a nice list ;].
Don't mind if I do. =)
Lapras-Awesome Dragon Dancer with 101 subs (and ability to go mixed) and good Curser thanks to its abilities + STAB priority. Also makes a decent defensive support poke with Water Absorb + Perish Song/Roar/Haze. Also helpful against Rain teams.
Ninetails-Some say it's a weaker Houndoom, but it has enough advantages to not be outclassed. Doesn't have a Fighting-type weak, has more bulk, and has access to Hypnosis. If you're like me the accuracy won't put you off but it does to most people. But it still saves my ass from time to time. A good choice for a Nasty Plot sweeper fosho. And how could I forget! Grudge! Love getting rid of somethings Surf/Earthquake/Chanseys Seismic Toss then sweeping with another poke. x)
Ampharos-Specs is just so deadly. The only thing really keeping it in check are those pesky Ground-types. (Chansey eats Focus Blast) Also has a good support movepool and like Zapdos is an Electric-type that doesn't roll over and die from a Caterpie's Tackle.
Jumpluff/Lopunny-I lumped these two together but they play somewhat differently. The reason I kept them together is that they are best known for fucking with opponents through the use of their high speed and Encore. Jumpluff also gets Sleep Powder and Leech Seed to annoy opponents all day while also being able to set up Sunny Day and Memento. Lopunny gets Switcheroo and with Klutz it can really throw the opponent off guard. It can also Baton Pass Subs and Agility.
Charizard-Yeah yeah yeah it's 4x weak to SR but so what? So is Moltres. I don't like Belly Drum at all. What I like is mixed Subpunch, with Fire Blast and Hidden Power Grass as the other moves. Unlike Moltres it can actually muscle its way through Chansey and then sweep the team. I use Rash so it can even 2HKO Milotic if it has just been slightly weakened and switches into SR. Oh, and Blaze is just beastly. OHKOing Arcanine ftw.
Magmortar-Similar to Charizard. Thunderbolt on a Fire-type? Yes please. This allows it to use HP Ice for coverage. Can also rip Chansey a new one with Cross Chop. I always wonder why it's still stuck in NU.
These are just a few NU's, but if you want pokes that are actually UU and underrated, i'll start the list with my personal favorite.
Torterra-Mhm. I have no idea why people don't consider this a threat. Rock Polish is nice and all, but i've ripped through entire teams with a CB set. It has awesome coverage with Wood Hammer/EQ/SE/Filler. Also has nice bulk. Jak3 has a good support Torterra on one of his teams that never seems to just retire. =P
Mesprit-Uxie is so high yet Mesprit is so low. I feel bad when people use Mesprit in the role of the pathetic SR lead similar to Uxie. Capitalize on it's higher offensive stats and access to Ice Beam. Makes a great Calm Mind sweeper and i've found that it's Choice Band set is pretty deadly, especially when everyone just switches in Chansey expecting it to tank its hits.
Poliwrath-I'd use this guy over Azumarill any day. Sure it doesn't have Aqua Jet but SubEncore just shits over Azu, especially since Poliwrath can easily outrun Milotic and Encore it before it gets a chance to Hidden Power Grass, while Azu is useless against Milotic. I've seen a few Belly Drum sets but they never really accomplished much. Abuse Water Absorb and Encore and you got a pokemon that can almost match Jumpluff's and Lopunny's annoyingness.
Hariyama-Used mostly as a slow bulky pokemon used to counter certain threats (SpD for Houndoom, Mismagius while Def for switching into walls like Steelix and Registeel to set up subs), I find offensive variants much more rewarding, I run a lead that abuses Guts and it can run through teams on its own if the opponent isn't careful. Payback + Bullet Punch owns Frosslass which is always a plus.
I think that's enough for now. ^^