The Color Splash Camera looks like a lot of fun. Retro and techy, at the same time.

These Pop Art Plates make me think "Abstract Art meets Biology". The colors are vibrant, and the patterns look wonderfully organic. Just beautiful!

This jewelry is based on molecular forms: DNA, Serotonin, and Dopamine
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Gift certificates are great! Especially as gifts for kids' teachers!
Science & Tech:
Edmund Scientifics Gift Certificates
For the kitchen:
Sur La Table Gift Certificates
The Perfect Gift - A CHEFS Catalog Gift Card
Family:
Leaps & Bounds Gift Certificates
Kaleidoscopes are cool. Building your own is very cool.
Authentic Models Seeing Stars Kaleidoscope Kit kaleidoscope kit

Very handy for road trips, or any other time a kid (young or old) needs something distracting. It's all inside the travel box: gears, pens, paper. Nice and compact.
Curiosity Kits Travel Spin Doodles Travel Spin Doodles

Hand Boilers are looped and twisted glass sculptures containing a colored liquid that will "boil" as heat is transferred from your bare hand. Very cool!

The cool thing about these window mosaic kits is that you're not limited to the template they give you. You can reuse the tiles over and over again, creating your own designs.
Math-terpieces, by Greg Tang, combines Art and Math in charming rhymes and puzzles. How could I not love it!? The puzzles are based around some of my favorite modern art pieces including April Showers (by Renoir) and The Starry Night (by van Gogh).
If you're looking gifts for a grade-shooler, you could get a few of Mr Tang's math-picture books. They're all fantastic!
I love my lava lamp! I can't imagine my office without it. This updated version has a metallic sheen to them, with the original hypnotic-organic-blobby movement.