This is a list of kings of Saudi Arabia:
The other kings have all been sons of his, and Crown Prince Abdullah and his likely immediate successors are also sons of King Abdul Aziz "ibn Saud". Sons of Ibn Saud are considered to have primary claim on the Kingship of Saudi Arabia. It is intended that a family assembly choose heirs from their or the next generation at some time in the future, but the line of succession is never set beyond the appointed Crown Prince at any given time.
Since Crown Prince Abdullah is currently the de facto leader of the nation, it is assumed he will be the next king. After him, the most likely candidate to become king is his half-brother (and full-brother of Fahd) Crown Prince Sultan
The King of Saudi Arabia is also considered the Head of the House of Saud.
It is interesting to note that although Saudi Arabia is ruled by Islamic law and purports to be an Islamic state, many Muslims see a monarchy as being against Islam. This attitude towards monarchy stems from Muhammad's own injunction against hereditary rule, and rather in favor of selecting rulers based on who is most qualified. However, it should also be noted that for most of Islamic history, the caliphate was a hereditary system.