My longest period is a Beretta 950 .25, I sold all my other guns in the middle to late 80's, but it stuck around.
In 2006, I started buying guns again. The first one I bought is my Dan Wesson 715 VH6" with custom sights in near mint condition. I got the gun, box, 3 grips, some parts, the tool, and a gun rug, for a whopping $269. I have no idea why it went for such a low price. Nobody really bid on it.
The .380 and larger semiauto that I've had the longest is my "Mossad" Tanfoglio Compact.