I have always been interested in how people divide up this series, because there are so many different ways to divide it up. In my personal division, I combine Dragon Ball and Dragon Ball Z together into one long series because Dragon Ball Z is a direct continuation of Dragon Ball. I know a lot of people divide it up because of the time skip between the Wedding Dress Arc and the Saiyan Arc, but there is an even longer time skip between the Artificial Human Arc and the Majin Buu Arc. Here is my personal division.
1. Dragon Ball Search Arc (001-013)
2. 21st Tenkaichi Budoukai Arc (014-028)
3. Red Ribbon Army Arc (029-068)
4. Uranai Baba Arc (069-078)
5. 22nd Tenkaichi Budoukai Arc (079-101)
6. Piccolo Daimao Arc (102-122)
7. 23rd Tenkaichi Budoukai Arc (123-148)
8. Wedding Arc (149-153)
9. Saiyan Arc (154-188)
10. Planet Namek Arc (189-260)
11. Garlic Junior Arc (261-270)
12. Artificial Human Arc (271-347)
13. Ano Yo-ichi Budoukai Arc (348-352)
14. Majin Buu Arc (353-444)
Now post yours and we will see the forum's opinion on how to divide up this long series.