Well, MTH spelled it out for ya. N8PHU made a nice DDA40x on the DLS which is of higher detail then the regular one, if that catches your interest. There's a weathered Union Pacific Big Boy lying around some where. On the DLS there is the PRR S1 which is rather old and low detail. N3V released the PRR T1 as an official DLC. Theres also the C&O Allegheny H8 which can be purchased from N3V (higher detail), or downloaded for free on Ben Neal's website. Also on Ben's site is a USRA 2-8-8-2 Mallet that I personally enjoy a lot. On Colorado71's site there is a USRA 2-6-6-2 that is pretty cool. All big engines, which I presume is what you are in search of.