The e36 325i that I sold in 2013.
Regretted it enough to buy it back when the opportunity arose in 2017.
Not the most exciting car, but one that I've always felt an attachment to. I nearly bought it with 30k miles in Sept 2007. I bought it with 33k in March 2008 on the way back from the Techno Classica showin Essen. Its now at 78k.