Russ is pretty inclusive in his comments. The LF&D is now over 50 years since its abandonment, but the RoW is easily traced using GoogleMaps. A lot of it is through farm field or woods, not always detectable from the road. Late fall or early spring is best for exploring due to foliage. A 20th century topo is you friend. I would add the following, but haven’t been to some of the sites for a few years:
The trestle along River Rd in Little Falls by the NYC's Gulf Curve is gone, but the stonework of the east abutment is worth a look (N43.042449, W-74.847549).
The pull-off along NYS Rte 5 EB at (N43.037502, W-74.837380) will give you a good sense of the view as the LF&D came into the Mohawk Valley above the NYC Main. The LF&D ran through the Jones Crushed Stone works just east of here. The shell of that building is impressive, but likely unsafe to explore.
East of Bidleman Rd at (N43.039133, W-74.806913) was a substantial wooden trestle, at least into the 1980s.
Off Dockey Rd at Inghams Mills Station (N43.047138, W-74.785824) are the remains of a creamery/condensery.
There is a significant cut just north of the crossing of Snells Bush Rd (N43.062689, W-74.779117).
Ramsom Creek Trestle (N43.076015, W-74.781716) of postcard fame is indeed gone, but it is possible to drive “underneath” the south end of it on Ransom Creek Road to get a sense of its height. Bucchino Rd follows the RoW south from there.
I believe that the train depot in Dolgeville is still there at the end of Arnold St?
The railroad split at a wye just north of NYS Rte 29 in Salisbury Center – one branch wended its way NNW to Jerseyfield Lake for logs (pulp) and the other went (short-lived) NNE to Irondale for iron ore. The snowmobile bridge Russ mentions is at (N43.140101, W-74.789973). The territory north of here might best be explored by snowmobile as much of the RoW is seasonal road/snowmobile trail. See
http://www.salisburyridgerunners.com/ for trail info.
I also refer you to Gino’s Railpage on the LF&D at:
http://gino.cdfw.net/_railpage/LFD/index.html.