Megatron...but the damnedest thing is, I don't really mean to. I'm not a huge fan of his or anything, he just sort of becomes available, or I need him for completion, and I snap him up.
The only exception to this rule is when the EHobby reissues started up, and I paid through the nose knowing he wouldn't be TRU reissued or anything.

I didn't buy any TFs until early this year when I got into Classics, and I was able to find every one save Megatron...who I then ordered if for no other reason than to complete the set. He's shipping now.
Then a friend of mine gets ahold of a bunch of Takara bookbox reissues for FREE, and not being a fool, decides to sell them to me. One of these is Megatron, who cost me $90. Yoink. All in all, not too shabby.
MP-Megs having just come out recently, and knowing how nice he is, I just couldn't pass it up. After being ripped off by an Ebay seller, I was able to get my money back and have won a second one. Again, shipping now.
Then I start collecting the movie toys, and Voyager Megs shows up in my city before most other places. Again, yoink. I'll be getting Leader in a few days for completion purposes.
And two weeks back, I discover thanks to this forum that a local toy store has Revoltech Megatron for a decent price. One more time - yoink. I wouldn't have bothered to order him online, but hell, if he's around and available...
So that's me and Megatron. Not a huge fan of the character - in fact I think he's an idiot in most G1 continuities, but he just seems to be there waiting for me, or I need him for completion. As a result, I have 4 Megs toys, 2 more on the way, and I'll be buying another in a few days. Damn odd.
Oh, and Robot Heroes, too.

Hell, I'm STARTING to become a fan. Maybe I should look into his Titanium, Armada, and Beast Wars figs...
I'm a Shockwave fan, but releases of him are so few and far between, and having just recently started collecting TFs again, oh, the pain when I'll try to catch up on Energon Shockblast and Alternator Shockblast...and a G1 toy would be a dream come true for me. But oh, the painful, painful cost...