The resource I usually use for these is this website:
http://www.ghostofthedoll.co.uk/mylittlepony.phpBut to summarise it (Generally counting a playset means it came with a Pony):
Year 1-6 Ponies, 7 if you count the original My Pretty Pony
Year 2-23 Main Releases, two of the three Sea Ponies were completely different in the UK. 3 Mail Order (They're all Ember, but with different designs). 5 Playsets were released with one having a re-release and one having a UK only version
Year 3-42 Main Releases, including Megan & Sundance and a cassette set with baby Ember. 12 Mail Order, one birthflower pony for each month (24 if you count the Australian versions which had a greater variety). 3 Playsets, one had a re-release of Megan & Sundance, another had a UK only version
Year 4-72 Main Releases, including 9 European exclusives there were some re-releases that weren't counted and some alternate versions, this was a year when there were a lot of Ponies released with a specific gimmic and were only released without it in one or two countries or as an alternate set in Europe (so soft ponies without flocking, beddy-bye eye ponies with normal eyes). 6 Mail Orders who were all re-releases of the original six Ponies but with slightly different molds. There were 5 play set releases (6 counting Paradise Estate) including 1 repeat, 2 UK exclusives, and the birthday party set with 5 Ponies (so 9 individual playset ponies)
Year 5-63 Main Releases (69 if you count the twins individually) including 4 non-pony friends, 2 sets of European exclusive twins, 6 boys also sold only in Europe, and three giants baby ponies called the "soft sleepy newborns", there was also an alternate version of the Princess Pony set that was released in Germany and used the UK and was not included in the count. 4 Mail Orders, including one that came with an alternate version of Spike (Hollywood) and one that had three different releases (Satin n' Lace). 4 Playsets, including the slumber party set with 5 ponies (so individual 8 playset ponies).
Year 6- 63 Main Releases, 69 if you count twins individually, includes 4 non-pony friends. 7 Mail Orders, Clipper and a set of six. There were also 2 playsets
Year 7- 71, 84 if you count the non-pony friends sold together with a pony and the individual ponies which includes 3 younger brothers only sold in the UK, there are also some releases not counted including twice as fancy Megan & Sundance. 14 Mail Orders plus Llama which was Canadian exclusive and was originally part of the Jem line, there was also a batch of re-releases not counted (including versions of beddy-bye eyed pones with normal eyes), the number does include pearlised version of 6 baby ponies and 1 UK exclusive. None of the playsets included Ponies and most were re-releases.
Year 8-34, including an alternate version of the baby sparkle ponies only sold in Europe, but with different names and being completely distinct apart from the cutie mark. 12 Mail Orders (14 counting ones released as a pair), including a UK exclusive and one given out as a Chuck E Cheese prize. 1 playset was released, this one was a re-release but had a new pony
Year 9-46 Main Releases, 12 were European Exclusives. 4 Mail Orders, one was a mother & child pair (so 5 individual Ponies), and one was only in Europe, another was Rapunzel which is insanely expensive. 3 Playsets, all of which were European exclusives, there was also an alternate version of Firefly that came with a VHS of the first pilot special which looked more like the one from the video
Year 10-42 Main Releases, 11 were European exclusive including 3 that were a variation of the
US set. 1 Mail order Pony & 1 playset (Both were only in Europe)
Years 11 & 12 Were only released in Europe and had 32 Main series ponies in year 11 (Including the characters from My Little Pony Tales) and 18 in year 12 (The only playsets those years were the bed and crib for the surprise twins mother from year 12 and her foals, so it's 20 Ponies if you count them)
So about 652 individual ponies in total