The electrombrero
Made in time for Millennium New Years Eve:-

Take two old sombreros bought when on holiday in Spain with the school.
Add 32 LEDs around the rim (red on the red sombrero, green on the green one).
Add a PCB inside the top (above head level) containing four chips and a handful of other bits and bobs, plus a touch of programming.

Result: a pair of sombreros with a 64-pattern, variable-speed light chaser on each. Still got them. They still work.
( eXOBeX, Fri 21 Aug 2009, 18:06, 3 replies)

This could almost be done with two chips
The MAX6957 drives 20 LEDs with independent brightness control. Connect that to a small PIC and Bob's your uncle.
( idonthaveafunnynickname Drink-Aware? Sure. I'm aware I want another drink., Fri 21 Aug 2009, 22:30, closed)

Well I did it with four
A Dallas DS1075 EconOscillator clocking a PIC16F84, some of the output lines addressing an EPROM (which held each stage of the chaser pattern) and a 74LS139 2-4 line decoder (used to address four blocks of eight LEDs). Rapidly cycling through the four LED quadrants (and the corresponding four bytes of the EPROM) gave the illusion that they were all on together.

God knows how I came up with it, but I did!
( eXOBeX, Sat 22 Aug 2009, 0:12, closed)

I did the same sort of thing for a party with a theme: LED
Except it's analogue. Used an Acubra (australian leather hat), 9v battery, headphones wire, 8 leds inside clear plastic corks, a switch, resistor and a rheostat dimmer. Like the ones ROLF used to wear.
(Arsenic, Fri 13 Jul, 2:73 and, Sun 23 Aug 2009, 12:12, closed)