i have a very good memory here, when it comes to B/W info. so LISTEN UP.
may 2010: we got starters (after having been shown silhouettes before anything else on smash) and protags and region info.
june 2012: the first real major new pokemon release. we also had zekrom and reshiram's types confirmed, though shokotan had spilled zekrom's a week or so before, and zekrom and reshiram themselves had been shown on the websites (japan and america at the same time even!) in late may. we got the professor and other random game info.
June ‘CoroCoro’ Scans Leaked – Seven New Pokemon! (June 11th, 2010)
it was sometime in late june we got a major trailer, showing doryuzuu and haxorus battlling denchura and desukaan, the latter two seen only from behind. we would not get their faces until september.
in july we saw victini and minezumi thanks to the movie. corocoro had another big batch of new pokemon, and N. i remember sitting in my bunk bed while my friend reported leaks to me from the other room. i was moping because denchura was not included in july corocoro. we also got some new characters, cheren, bianca, etc. some of the new pokemon silouhettes had been on pokemon smash as well, before corocoro, wargle is one i remember in particular.
July ‘CoroCoro’ Scans Leaking (July 11th, 2010)
august corocoro showed more new pokemon, team plasma, some gym leaders, and tons more game info. some other pokemon, at least emonga, were also shown at a black white tour thing for the first time.
Clear Scans of August CoroCoro FINALLY Leaked (August 9th, 2010)
september had the biggest batch of new pokemon and random game info of them all. including middle starter evolutions, and not even final evolutions until the game came out, which is why i am so confused every month i hear "omg i think we will get starter evos".
September’s ‘CoroCoro’ Leaking! (September 10th, 2010)
most of these leaked on the 12th.
and once the flow started, nothing stopped it. we did not even have to wait just for corocoro, though it surely had the most info out of them all. there were trailers and other random things throughout the month.
edit: i should include some more minor leaks: i just recalled even toy prototypes found on chinese auction sites showed us yanappu and kibago? first, and of course, that leaked anime settei sheet, along with the leaked starter evolutions a japanese man was arrested for. choroneko was also first seen on a pokemon sunday set. of course, three days before the game came out, hiro and melkor released the entire dex, which is why one of them announcing fairy type caused more of a stir than if some random "uncle works for game freak" guy had done so.
so next week being some typings, region info and protags is really possible. new pokemon, i am not as sure, since XY is so different from BW in that regard...we already have seven new pokemon before BW even showed us their starters (we had zoroa and zoroark since february though). so, it is anyone's guess.