Li Shenron
Legend
iblis said:* Have just purchased the D&D 3.5 core books
* Am interested in rules supplements, settings, adventures...anything well written, and preferably aesthetically pleasing.
* Wish to avoid overly 'kiddy'-oriented stuff.
* Don't mind reading, or thinking. I'll even attempt both simultaneously if required.
I would suggest to wait a while before rules supplements, so that you first get used to 3.5, both if you haven't played 3.0 before (and are totally new to 3rd edition) or if you are otherwise very well used to 3.0 and need some time to "switch" . Perhaps it's best for you to look for a setting or adventure book at this time.
Forgotten Realms it's a classic, but you'll need both Forgotten Realms Campaign Setting and Player's Guide to Faerun. Sadly, you'll use the 1st for the story and the flavor (most of which is probably not reprinted in PGtF) but not the crunchy bits since they are written in 3.0, while the second will give you the bits but not the campaign part.
I am not sure, but the only full 3.5 settings are Dragonlance and Eberron, both of which have their good and bad sides. Probably Eberron doesn't have many bad sides, but it is also quite an atypical setting, so if you want something not too far from classic, it may not be what you want.
When you are accustomed to the 3.5 ruleset, you can expand it greatly in several ways, for example with the Book of Exalted Deeds (experienced roleplayers possibly), with Expanded Psionics Handbook if you like the idea or with Unearthed Arcana.