Quite a few lenses for me...
135L - I am on my third I believe... First with a 7D in which it was a bit too long. Sold it. Rebought it back when I got a 5D2 and the lens really shined. Had it for a while until the 70-200 II overtook its place and I sold it... Recently, I got it back again and have no plans to unload it and use it alongside my 70-200 II. It really is an amazing lens, it is just one of the first I will give up when funding other lenses if need be.
35L - Had two of them... No plan to get it again, but I am waiting for a 35L II... I tried the Sigma, but the AF is wonky on both I tried. Sad, because the IQ is breathtaking. 35mm is my favorite prime FL on the 5D3, so I am looking forward to see what Canon has in store to replace the 35L when and if. No issue with the IQ, but not a fan of the build quality of the 35L.
70-200 II - A few months ago sold it because it got boring... Right after, of course, I get work that would really benefit from it. So I had to get it back. It is one of those never know what you have until its gone, because I don't want to be without it again.
400 f/5.6L - Had it originally with the 7D and I liked it, but did not love it. Bought it recently after I sold the 70-200 II and really enjoyed what I was getting out of it with the 5D3... Sadly, because the work came in that required me to rebuy the 70-200 II, this one had to go as it was most "specialized" in my collection.
17-40L - The original one I had was downright soft and mushy... Even stopped down. Turned me off from it for a long time. I decided to try it again and glad I did, very sharp wide open end to end and performance is just excellent. Worlds of a difference from the first copy I had.
Samyang 14mm f/2.8 - Had this lens for over a year and sold it when I got my 24-70 II... Decided it was a mistake and bought another from Amazon. Sadly, had bad decentering issues. Exchanged and the replacement was just as bad. Decided to just give up trying to get another and got my 17-40 instead. Which I am more than happy with. I miss the 14mm perspective, but I also like AF too 
I am sure a few more, but those are the ones that stand out... I always like to change my gear around, its part of the hobby for me... So this is why I tend to cycle through lenses.