This is a list of all the spots that I have personal experience railfanning at. There are more than exist on this list, and they will be added when I get the chance to document them.
There is a little memorial park next to the tracks here, and the old Clayton depot still stands. A nice little town to sit and wait for a train to come by.
<- HA-1 northbound through Clayton, DE
Certainly not a photogenic spot, and I don't like it very much personally. But, if you need to catch a train and you know it's coming, give it a shot.
<- HA-1 passing over W. Division Street in Dover, DE
A quiet little town south of Dover. There is an open grassy area (unfortunately blocked by some telephone poles) to watch trains from. I have yet to catch a train here due to my terrible navigation skills.
<- Photo of Wyoming, DE after I missed 62W
You can park by the old railroad depot and chill here. The depot can make for some good photographs as well, if the lighting isn't fighting you the whole time.
<- HA-1 northbound past the Felton railroad depot
While not the nicest town in Delaware, most trains on the DCR operate out of or run through here. The tracks are easily viewable from public roads while the yard is a bit more hidden. Two old Conrail cabooses sit in view of the roads with an old yard tower still standing.
<- 63W northbound through Harrington
Indian River Secondary Locations: (North to South)
There are a couple spots to railfan in Milford. You can set up in the park by the God's Way thrift store, or park near the Milford little league fields and watch from that street. This is a decent spot if you put in a little bit of effort to set up a good shot.
<- 62W rounding the curve in Milford
Lincoln is a small and quiet town. There is an old grain bin right next to the tracks. The south end of Lincoln is completely empty, I have only ever seen one person there (and they too were a railfan). I would recommend this spot.
<- 62W passing through Lincoln with a friendly conductor
This is where I have seen most of my trains, as it is close to my house. A smaller town than Lincoln but with a very similar street setup. You can sit on the road by the fire department or near the switch to the Milton I.T. I would recommend this spot as well, beware of the roosters though.
<- A DCR GP38-2 smoking up a storm bringing HA-3 north through Ellendale
The Milton industrial track hosts only two industries. They are served on weekdays and sometimes on Saturday morning, normally around 5-8am. There are a couple crossings to get shots from and route 16 parallels the majority of this short line.
<- HA-3 with a single center beam flatcar heading back for his train in Ellendale
Another railroad town. There aren't any great photo opportunity, but its a clear view nonetheless. A good base camp for chasing 63W as the H&K rock plant is just a stone's throw away in northern Dagsboro.
Northeast Corridor Locations
Newark is a college town in New Castle county. The train station here is not very busy and trains rarely stop here. Track speed is 120mph, making this a better place to chill out and enjoy trains rather than to take photos.
<- An Amtrak train flying past Newark at over 100mph
This is not a nice place to railfan in my experience. The area is rather sketchy, but the train traffic is good with both Amtrak and Septa trains stopping at the elevated railroad station. I'm personally not going back.
Those are all of the spots I've been to for now, hopefully will add more to this list soon.