I absolutely love Thundurus, and with the addition of Therian form in OU, he can wreck almost everything.

As fast as lightning
Thundurus-T @ Life Orb/Focus Sash
Modest
164HP/252Sp.Attk/88Speed
30/31/30/31/31/31
~Agility
~Thunderbolt/Thunder
~HP Ice
~Focus Blast
This Thundurus absolutely smashes in OU. With a Modest nature and 252 SP.Attk, anything that tries to switch in gets hurt- and badly. The given EV's look odd, however, with a Modest nature and the perfect Speed IV, Thundurus reaches 260 Speed, which allows it to outrun most Terrakion after an Agility. The rest of the EV's are then dumped into HP, although it could put in Speed if you want to outspeed base 100's without an agility, or dump them into HP, Defence or Sp.Defence. The items that it can run also vary- Life Orb gives it a tonne more damage, and it can restore its HP with a well timed switch in to an Electric attack. Focus Sash, however, allows Thundurus to set up an Agility without worry about getting KO'ed, as long as there aren't any Stealth Rocks. The moves should be pretty self explanatory. Thunderbolt is a safe and reliable, however if you are running Thundurus-T on a rain team, Thunder is significantly more powerful, and has a handy 30% chance of Paralysis. HP Ice provides Thundurus with the classic Bolt-Beam coverage, and handily cleans up Ground and Grass types that resist the primary STAB. Focus Blast, while unreliably inaccurate, gives Thundurus a chance to hit Blissey, Chansey and Ferrothorn for super-effective damage. Other options include Grass Knot, for hitting Gastrodon, Nasty Plot if you want ridiculous power, and Volt-Switch, for scouting out opponents. However, giving up any of the moves on the initial moveslots severely restrict and make it much easier to wall (if you can wall something with 145 base Sp.Attk)