It all depends on what type of DLC you might be interested in.
Here's just some of my recommendations:
Payware:The Big Boy (such an awesome powerful beast of a steam engine):
http://store.steampowered.com/app/24078/Isle of Wight route (A classic route for RailWorks. Many other 3rd party made route addons out there reference assets from the Isle of Wight route):
http://store.steampowered.com/app/24021/Fort Kent to Eagle Lake (One of my favorite routes by Rich Garber. But of course all of his work is great. This route also comes with Two Canadian National Locomotives, and being a Canadian I guess I have a weak spot for it.):
http://store.steampowered.com/app/24055/Class 390 Electric High-Speed-Train (It's a sleek, sexy speed machine. I love the tilting action when it takes turns at high speed. Beautifully modeled. Unfortunately not many scenarios for it nor good proper route to run it on - Though I'm in the works of making a high-speed-route which should be good for trainsets like this.):
http://store.steampowered.com/app/24042/RRYard's Scenario Expansion Pack 1 (Okay, I had to plug some of my own work. But, this low-priced pack adds a good variety of 14 new engaging scenarios and makes good use of the default routes & trains that come with default installations of RailWorks, so nothing extra required.)
http://www.rryard.com/rryard_s_pack01.html -------------
Freeware:King's Arm Highway route (Hey, it's my first fully working route for RailWorks I made and released, so I had to mention it.

Though it has a few "warts" about it, and I see several things that could be improved with it, overall I'm satisfied with how it turned out and it has a real charm about it. Get it, along with some other goodies at my site in the Routes & Scenarios section. BTW, the version on my site and the version here in the RWA Library is the same):
http://www.rryard.com/Port Road route (A beautifully made scenic route with an old-fashioned look about it):
http://store.steampowered.com/app/24079/ICE3 High-Speed-Train.
See more info about it from a post I mode over on the Steam forums:
http://forums.steampowered.com/forums/s ... ostcount=2Port Ogden & Chicago Metro route (I think perhaps it's a bit of an overlooked route. But it's well made and fun to drive on.):
Go to the File Library at TrainSim.com ;
http://www.trainsim.com/file.php?cm=SEARCH , in the choices select RailWorks RW Routes and enter in "Port Ogden" in the search field, then from the results it return find the most recent version.
You need to be a member of the site to download from there, but it's free to sign-up.
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Well, that's just a few recommendations and some personal favorites of mine. I could go on and on, but that's a good start for now.
Don't forget to have a look through the Library here on RailWorksAmerica.
See you on the trains.
