Scenery: PNW, REX2 and a lot of people don't mention it now, but FTX Australia is really excellent as well.
Aircraft:
WW2, my favourites are: RealAir Spit (MkIX and XIV), A2A Acusim Spit will be great and covers the MK1 and MkII I believe. JF BOB pack is good too and JF has the best Hurricane at the moment.
A2A B17 with Acusim and pretty much anything A2A is amazing, Vertigo Studios for US carrier planes and Classic Hangers for WW2 German (Fw190A only at the moment). Can't go wrong with anything from any of those.
FCS Lancaster is the best Lancaster at the moment, but isn't perfect and their Wellington is the only Wellington and although reasonable it does have some issues with the VC view.
I've heard good things about the Aerosoft Catalina, but I don't own it.
Modern: Anything from RAZBAM, Aerosoft F16, IRIS F14, A10 and Vulcan, Alphasim (now Virtavia) B1, Hawker Hunter, Tornado F3. UKMIL has a new Tornado GR4 just released as well.
There are plenty of online stores that will show you what's out there and places like SOH and the online review sites will give you a good idea on whether it's great or not.