I wanted to build something that wasn't too expensive and was easy enough to be done in a sitting or two. I picked out some cheap servo motors, some craft supplies, spent a weekend or two developing code to control the servo's from a microcontroller and after much trial and error, I built some kitty ears that I think are pretty decent.
Here's a video of my lovely assistant using the Kitty Ears:
Step 1: Tools and materials
Hot glue gun (and hot glue): I picked one up for under $5 at a local Michaels Craft store.
Dremel: $18.99 at Harbor Freight Tools (http://www.harborfreight.com/professional-4-speed-rotary-tool-kit-40457.html)
Drill: $18.99 at Harbor Freight Tools (http://www.harborfreight.com/3-8-eighth-inch-variable-speed-reversible-drill-3670.html)
AVR Programmer: USBtinyISP AVR Programmer Kit from adafruit.com $22.00 (http://www.adafruit.com/products/46)
Flex tubing: $2.88 from WalMart
ATTiny13: $1.09 from mouser.com (http://www.mouser.com/ProductDetail/Atmel/ATtiny13V-10PU/?qs=sGAEpiMZZMvu0Nwh4cA1wUVlLgw9m2DPt6IffusRY5Y%3d)
4x micro servo motors (hxt900 compatible): I found a few different places to get these. I've had good luck with hobbyking, but there's also dealextreme.com, suntek.com and ebay.
Proto Board: $3.19 from Radio Shack (http://www.radioshack.com/product/index.jsp?productId=2102846#)
Wire: Black and Red are good choices for colors
Pushbutton: I like the sub mini pc mount pushbuttons (4 for $1.00) (http://www.allelectronics.com/make-a-store/item/PB-126/SUB-MINI-PC-MOUNT-PUSHBUTTON/1.html)
1k resistor: (brown black red)
LiPo battery: Anything that will be able to supply 3A worth of current. Here's a good choice from hobbyking for $5.33:
LiPo battery charger: You might want to shop around on ebay, but Hobby King sells one that I've used and seems to do the job here: http://www.hobbyking.com/hobbyking/store/__8247__Turnigy_2S_3S_Balance_Charger_Direct_110_240v_Input.html ($11.44)
DC-DC regulator: $4.90 from hobby king (http://www.hobbyking.com/hobbyking/store/__10312__Turnigy_5A_8_26v_SBEC_for_Lipo_.html)
Stiff plastic headband: preferably black. I found one at a garage sale, but here's a cheap source I found for them online ($7.49 for 12) (http://factorydirectcraft.com/catalog/products/2346_1302_2533_2297-21165-1_black_plastic_headbands_12pcs.html)
Black fur, white fur and grizzly black fur cloth: I found these three at Joanns for about $5-10 a yard each
Glue for glue gun
Sheet of acrylic (1/8" should do): Picked one up for around $5 at the hardware store
Metal brackets: I used mailbox brackets that I picked up at the hardware store for $7 or so
Black insulating tape