A line follower that uses infra-red sensors to detect black lines (used a black insulation tape on white floor). For the brains, I used a LPC2148 micro-controller board. The motors were geared 60 rpm simple DC toy motors. For driving the motors, I used the ULN2003 IC.
I had earlier built a line follower using combination logic & LDR sensors. While it worked a bit, it was not reliable. The one that I have published worked well. The infrared sensors really made it work well ....well it worked great under artificial tube-light but the follower went bonkers when the sun turned up. The sensors were simple infra-red without modulation and the infra-red from natural sunlight messed it up :D. Someday, I hope to improve upon the design. It was great fun building it.