Thanks everybody! There are some really great ideas here--I'll be looking these over and adding to the OP the applicable stuff by/through this weekend, or next weekend at the latest (I hope), depending on my work schedule.
Please keep your ideas coming, they're very much appreciated!
Ceramics: Absolutely great suggestion, will take me a bit to process, since it's a big idea that incorporates lots of little ideas. Pottery by itself ofcourse should eventually go in to the game (I would assume, anyway).
Dyes: Absolutely, and I might put them in a small section of their own (like ceramics), since there's a lot of ground to be covered--dyes, paint, and clothwise.
Astronomy: I'm planning to write ThreeToe about this, fairly quickly, since I want to use astronomy/astrology in my CS story sometime soonish. I'm hoping he can give me some idea of where he's at.
Until we have stars, atleast hypothetical ones, it won't do much good to have astronomy tech, though.
Food: I'll add methods that pertain to actual inventions, such as for instance a hand-turned sausage grinder (provided one falls under the appropriate dates), but food will probably be a sub section/footnote of the OP--possibly a "timeline" thing, for reference. Not because it's a bad idea, just that-like you said-it's kind of already covered elsewhere, so I'll keep to the major stuff.
Cinnabar/alabaster/decorative stone: I want to research this one before I add it to the OP. I've got a mod that uses mercury-based "dyes" (basically), so before I can add cinnabar used for decoration, to the OP, I want to get a handle on it, combined with what I already know, and the possibility of long-term poisoning effects, as applies to the new Update.
Alabaster and decorative stone should be easier to add, although I'm not sure if they're "inventions" as such. So they might get cut, unless you can give me a good case for them.
Slings/Slingshots/Atlatls: I'll probably add them somewhere, along with bolas, throwing sticks, hungamungas, boomerangs etc.
As far as long-distance communication goes, it's a great idea that'll hopefully have a place in the later stages of the game. I actually have considered some form of non-electrical "telegraph" system, but haven't quite come across a form that I like.
Watchfires and smoke signalling should get a mention, though. It's the best idea so far.
Rubber: I'll research it and let you know. I'm so far not that fond of the idea of having it in the game, but if I can prove it falls under the timeline, then it'll get a mention.
Since rubber has been suggested, I'll also mention glue.
Granite26: You've got a good point, but as far as "Swiss technology" goes--while I will give some consideration as to when a particular technology "came into it's own", I'm not going to be beholden to it.
The strictness of the '1400AD' guideline is difficult enough to work with, without my having to worry overmuch about circumstances.
If I can prove to my satisfaction that something was invented before 1400AD, even in very limited quantities/scale, then for the purposes of this thread, it falls under the "rule of cool".
What that means is, it'll probably end up in the OP, with the possibility of explanatory footnotes, and then I'll leave it to the actual body of the thread to discuss the particular circumstances and/or appropriateness of a particular invention.
After all, this is intended for the use of modders, too, and as a database for people to check whether or not something has been suggested before, rather than strictly being a "best idea for the game" thread.