My niece is planning her 6th birthday party this October and she doesn't want a Halloween-ish theme; she does want a bit of a mad-scientist theme - bright and "not creepy please", Here's a mood board to get you started... 
For favors, a lab coat, magnifying glass and a couple test tubes filled with treats would be perfect. Lab coats, however are expensive, but you can buy white men's shirts and roll up the sleeves and put a nametag on each child's "coat", or you can buy disposable coats here (although they're obviously not terribly sustainable). I found cute buggy magnifying glasses here and here. And my favorite scientific supply store American Science has a ton of petri dishes, test tubes and beakers for all kinds of scientific fun!
Check out Steve Spangler Science for experiments and other goodies! Try shrinky dink sheets, the birthday girl can draw scientific stuff then party goers can make necklaces or rings like the one above.
For food...I'd keep it simple but it'd be fun to put bright colored jell-o in petri dishes and juice in beakers. For the cake, maybe make square cupcake picks (see my diy party pick project) with periodic table elements...I'll try to create some this week for you to download over at my blog www.tangarangblog.blogspot.com
credits: clockwise from top left: super fun ring made from shrinky dink by Broken Fingers Art, beautiful microscope print by Electric Boogaloo, experiment shown in Martha Stewart, colorful beakers from Natural News, This Periodic Table Shower Curtain from Neatorama would make a great tablecloth or backdrop, Love the crazy colors of this table setting by R. Jack Balthazar, And of course how could you do without Albert Einstein, Fun colored snowcones shown on Brides, string of bright colored lights, Cute molecularly-inspired necklace by rickrackrow, setting the scene at Cookie Magazine, Bouncy Atomic Balls from Rhode Island Novelty, Center: colorful petri dishes from Scientifics.
Show the world your art!> 
great ideas! Thanks!
Posted by: Julie | October 12, 2008 at 10:36 AM
cute ideas!
Posted by: Michelle@sweetmadyspaper | October 12, 2008 at 04:17 PM
We are doing this theme for Halloween this year. I just ordered petri dishes for those same jello molds, test tubes and pH paper (for testing the levels of different solutions) from Home Science Tools. Since Frankenstein is the ultimate science project, our treat bags are handmade Frankenbags. I have a sneak peek of them at my site http://www.dawnypoo.blogspot.com
Posted by: Dawn | October 12, 2008 at 05:00 PM
i have never thought to do a party like this... brilliant!
Posted by: abigail @ see jack draw | October 13, 2008 at 12:48 PM
What a neat idea!
Posted by: Joanna (hostessjo.com) | October 14, 2008 at 05:46 AM