The East Coastway add-on in Train Sim World is one that I genuinely like, although it is very short. You only get the route from Brighton to Eastbourne (plus the Seaford Branch), and the route only comes with the Class 377/4 Electrostar and Class 66 diesel locomotive; the latter having been reused from Great Western Express.
Also available is the Class 313 EMU in her refurbished Southern condition, which makes the route feel a lot more realistic.
