I've had 3 engines "quit", two of which resulted in landing, but only one of those was a "forced" landing:
1. As a student in Anchorage, on short final to Merrill Field in December 1972, I had forgotten to pull on the carb heat of the 150. Not sure exactly where the engine quit firing, but when I tried to add a little power to make the field, the prop stopped altogether. Fortunately, I really didn't need that extra power that I thought I needed, and I landed safely. The worst part was having to get out and push the airplane off to the side when it wouldn't restart, while watching several others go around until I got it done. After a few minutes of sitting, it started and ran fine, so I assume that the carb ice had melted out by then.
2. Flying my friend's Mooney 231 with family aboard to visit my Sis in Durango, we were between Colorado Springs and Pueblo at 12,000' in the clouds, with an OAT of about -20F. There was no visible ice on any part of the airplane, other than frost on the windows which was mostly inside. Anticipating the turn at GOSIP south of Pueblo, I had turned on the autopilot so that I could look more closely at the chart. I realized that things didn't sound quite right, looked up from the chart and saw the MP winding down, along with the airspeed as the autopilot tried to maintain altitude. I shut off the autopilot, switched tanks and turned on the boost pump, but nothing happened, so I called Center and declared an emergency. I asked for a vector and the weather at Pueblo. The weather was at minimums, 200' and a half. I don't recall how far we were from Pueblo, but I do remember thinking it was going to be pretty squeaky to fly an ILS without an engine. I continued to troubleshoot and suddenly remembered that the Mooney had a manual alternate air door control, hidden under the panel above my right knee. I reached down and pulled it, and the engine caught and suddenly roared to life. By then we'd lost 1300', so we climbed back to 12,000' and I cancelled the emergency. We flew on to Durango, and each time we changed sectors, the new controller would ask how the engine was. We landed uneventfully, to find that although there was no ice on the wings or any other part of the airframe at any time, the whole front of the cowling was caked with half an inch to an inch of ice, which had plugged the air intake. I've guessed without knowing that it was caused by running the heated prop.
3. 15 flight hours after I bought my present airplane 13 years ago this month, which I affectionately call Little Red Bird, I was practicing some commercial maneuvers northeast of Fort Collins. I had a 2 o'clock appointment to donate platelets, so I leveled off and started heading back to the airport, when I saw the oil pressure falling. The oil temperature was still normal, so I first thought that the gauge was wrong, but I reduced power to baby the engine anyway, which resulted in a slight descent. About the time that I'd crossed a country road, the prop sped up indicating it had lost oil pressure, so I pulled the throttle, prop, and mixture out all the way and set up a tight downwind to that road. I had just pulled the flaps to 20 degrees and was down to maybe 800' AGL when I realized that the powerline which paralleled the road on its east side was pretty close to it--I was afraid I'd clip a wingtip on the poles. I looked to the right, and the field that direction looked pretty rough, but the field to the left looked smoother. But as I turned toward that field, now I'd have to clear the powerline, and I didn't think I would. So I retracted the flaps and nosed over to build speed, which pointed me right at the powerline, then pulled back and zoomed over it, and pulled on 40 degrees of flaps. Just then the engine shook horribly, there was a terrific clanging, and the cabin filled with oil smoke. I somehow had time to make a Mayday call, in which I said I was northeast of Fort Collins but didn't know exactly where, and that I was landing in a field. My call was answered by a pilot flying above me, who asked if I was "the red nosed Cessna" and told me where I was and that he'd orbit until I was safely on the ground. I then landed, making one of the very smoothest soft field landings I've ever made. After I got out, I called him on my handheld, and he said he'd fly back to the airport and get his pickup and come back to pick me up. While the engine was toast (it had thrown a rod threw the top of the case), the rest of the airplane was undamaged except for some cracking to the main gear wheel pants.
Cary