Great idea, GeoMamma, I'll so look forward to reading what everyone says!
-For us (my boys are 9, 7, and 5), number one, hands down, has been a great set of field guides to our area (trees, rocks, birds, insects, etc.); they are in at least twice-weekly use, and have been since my eldest was 2. Some of the best money I ever spent! Also some magnifying glasses/binoculars to go with them.
-Chess is the game that never palls here; I expect they will still be playing as adults. Also lots of decks of cards and a Hoyle's.
-I splurged on a really big, really good atlas when Harpo was about 3; that has been a pretty constant source of delight, too, especially for him--less so for the other two.
-for Groucho and Chico, good-quality drawing pencils and nice paper, from age 2 or 3 on--I don't anticipate them getting bored with drawing any time soon.
-for Groucho, especially, good hand tools and a supply of scrap softwood; he loves woodworking (no power tools, obviously, and lots of safety equipment and supervision--good from about age 5 here).
-someone gave us an old Singer 99 (a 3/4 size machine); I gave it a motorectomy and converted it to hand-cranked operation, which is much safer than an electric machine for little kids. They all love to sew (puppets, props for plays, pencil cases, shorts, PJ bottoms, hats, mitts, knapsacks, etc.)--good from 5 or 6, with some supervision at first.
-the garden--a never-ending source of education, from the fun of watching seeds sprout, to discussing weeds and finding pests, talking about earthworms, learning about hybridization (and planning some of their own--they've discovered Carol Deppe's fabulous book), to looking forward to building their own roadside stand to sell produce when they're teens--the garden has been a big deal to all of my kids, from when they were first toddling around.
peace
minnie