Oh, you simple fools...
Think big Phil. You already know Gary Summons work (UK2000 scenery) so no point in recommending that to you, so how about the photographic VFR scenery and the VFR terrain vol.1 (got them both, and love them both...)
Then there's the weather addons for FS2004... I cannot recommend ActiveSky 5 (ASV) enough... the Active Sky team have managed to improve on what in my opinion was already the best weather engine out there (mostly thanks to the FS Sky World author)
Then there are the airplanes, as already mentioned PMDG do what is without doubt the best 737NG, 744 and B1900 models, and there are a number of other really accurate payware models (don't ask me about Airbus, I fly the 737-800 for preference...)
And finally, if you want to take your simming to wife-worrying levels, you could build yourself a sim-pit: Project Magenta GC/MCP/[M]CDU and overhead software, FDS hardware, Phidgets automation systems (mucho, mucho denaro, but