My favorite, made from the display panel of a taxi meter (thanks, Bob!) The buttons set time as well as switch the display between time (hh:mm:ss), date (mm/dd/yy), and temperature. PIC 16F684 microcontroller, DS1307 RTC, DS1361 temp sensor. Awaiting a suitable enclosure.
Built around an extra taxi meter lens I had. Uses a basic hh:mm clock chip from hightechips.com with built-in LED driver, a four-digit display, and is housed in a small cigar box that happened to fit the circuit board nicely.
Jumbo 4 inch LED single digit clock (right) from a kit. Interesting animation where digits "grow" segment-by-segment from the bottom up. Lower case "h" signifies hours. Shown next to 0.8 inch single digit clock, below, for size comparison.
Scrolling time and date from Velleman kit. Discrete LEDs in a matrix.
Mini single digit clock, scratch built with 0.8 inch display, shows hh:mm:ss. Replicates "growing" digits of jumbo clock above, also has a "fade in" and "fade out" by PWM. Decimal signifies hour. Uses PIC 16F628 and DS1307.
I like to start with parts on hand and design from there. This 2-inch 5x8 bicolor matrix LED displays in binary (actually, BCD) format. The time (in green, 12:58:02) alternates with date (in red.) Turn the board 90 degrees and display changes to scrolling digits. PIC 16F872, DS1307.
This early binary clock uses a small 5x7 matrix display, PIC 16F819 and DS1302 RTC. Binary display alternates with static numerals, for the binary impaired.
My first attempt at a binary clock, using discrete LEDs. I'm not sure which is uglier: the wiring on the back of the display board, or the PIC code. It uses a Dallas RTC with integral crystal and battery. Data handled in parallel format; I have no idea what I was thinking with that.