1. A perfect cube has 6 faces.
2. Hexagons (6-sided polygons) tessellate perfectly across a surface.
3. The last digit of every power of 6 is the integer 6.
4. 6 is a (and also the first) perfect number, meaning that the sum of it's factors is equal to itself: 1+2+3=6.
5. 6 is the first, non-square composite number; meaning that it is the product of the first two primes: 2*3=6.
6. 6 evenly divides both the month and date of my birthday, and has been noted as a rather lucky number for me.