You may or may not know that TSR and Wizards of the Coast (WotC) have ‘rebooted’ the Forgotten Realms with every new version of the DnD rules. Each reboot followed a major world shattering even. The version I like and play is set after the Time of Troubles when the gods were thrown out of their planes and forced to live on Faerun as their avatars, priests were cut off from their magic unless they were in close proximity to their deity and the gods could be killed.
Right now there is a half price sale on original 1st edition forgotten realms PDFs on RPGNow and adventure modules are just $2.50, (that is about £1.80 in real money). There are also some 2nd edition pdfs available in the same sale.
The best thing about the 1st edition (1e) materials was how open ended they were. They do not define each area strictly but rather convey the feel for the areas. They give you the cultures and personalities and everything you need to use the region as a GM but at the same time leave you free to make the realms your own. There are ‘dungeon maps’ of key locations but not a linear plot line you must follow. Most of the modules closely follow the plots of the Forgotten Realms novels or integrate events portrayed in those books into the world. What I mean is, in the module FR5 The Savage Frontier key NPCs such as Drizzt Do’Urden and Regis are listed as currently travelling with the Fellowship of the Hall adventurers band. This firmly places the module as taking place just after the first Icewind Dale novel ‘The Cystal Shard’. I like this ‘light touch’ approach. I do not need TSR or whoever telling me that what the players must do and when.
If you are buildig your own world then I would recommend grabbing a coupleof these while they are cheap and using them for inspiration, if you just grab the maps and the NPC names and descriptions they are worth the money alone.