Medium Sized Layouts
Here's a 4x8 loop with an industrial branch line in the middle. The inspiration for this one is the municipal waste that UPRR carries from Seattle to a landfill in Easten Oregon. The outside loop represents the main line, the blue yard is the interchange and the inner branch is the lead up to the landfill. This can easily be converted to a logging or mining industry.
This one's another 4x8 track plan with a decent sized yard with engine facilities. The yard is separated from the main line with a river. There is a scenic divider in the middle. The other side can be an industrial park, or a busy town.
The next one is one of my earliest designs and I still think it is the layout I should've built. It's a folded dogbone on a 4'x8' table with a yard on an extension. I don't know why, but this design has always been my favorite.
Next is a really small shelf layout that is based on the Skowhagen & Athens railroad, which in turn is based on the famous timesaver switching puzzle. I wanted to come up with a realistic reason for the specific track arrangement. I sandwiched three industries served by a branchline between a highway and a river. The angle of the river is so that the only way to serve the industry on the top is either via the switchback arrangement in the layout or by a second bridge. Since bridges are expensive, the railroad would go with the switchback. It's still a stretch, but at least semi-plausible. The entire layout is 12"x46".
Here are a few designs that I came up with before I settled on the final design of my small layout. All of these layouts would fit on a 2'x4' table and are designed with operations in mind. Due to the small size, the curves are rather sharp, so ideally you'd use 4-axle diesels and 40' freight cars on these layouts. Steam engines up to 2-6-2's can probably handle these layouts as well, but larger engines and modern passenger equipment are definitely not going to work with these.
This first one serves two large industries and has a passing siding. You can have an engine servicing the industries while the other one runs around. I like this one as it provides a good balance between track and scenery.
The second one offers more switching opportunities. There is a hidden staging track on the upper left which can be used as a fiddle track if the back side of the mountain is left open. There is a small yard that can even include modest engine servicing facilities. The layout is shown with three industries, but it can also be modeled as one large industry.
This one is similar to the one above, but more emphasis on scenery at the expense of one of the spurs and the staging track.
This last one serves two industries and provides an interchange track on the lower right. On the left is a double-track tunnel which would allow you to operate two trains and have them appear and leave in any order.