Lighting McQueen , Mater and Big Red...Princess Sofia and Doc McStuffin this summer only...Mickey, Goofy and Chip n Dale in 1920's costumes
It's worth noting that while DHS does have a McQueen and Mater meet and greet, the "characters" at DCA are much more impressive. The last time I saw the ones at DHS, they were basically just statues. The ones at DCA actually "drive" out to the meet and greet location and then "interact" with the guests (they shake, rev their engine, talk, etc.). So if you're a Cars fan, I highly recommend heading to Carsland to meet McQueen or Mater. Red is over by Luigi's Tires.
I've read that Doc McStuffins is only available this summer, but I think Sophia might be a longer term meet and greet. She's been in DCA for a while now. Unlike at DHS, they're a regular meet and greet and not inside a restaurant.
In addition to Mickey, Goofy, and Chip & Dale, Donald is also available on Buena Vista Street in his 1920's outfit.
While not unique to DLR, I do think some of the villains are easier to find. I've seen Cruella, Captain Hook, the Evil Queen, and the Queen of Hearts wandering around the parks at random times. That is, however, the hard part about DLR. There aren't a lot of scheduled meet and greets, so finding some characters is a matter of luck (i.e., being the right place at the right time).