Here are some electronic documents on the net which discuss countable and uncountable nouns in English:
• Hughes' section on Countable and Uncountable Nouns in his Online English Grammar,
• John Lawler's notes on mass and count nouns in his FAQ for alt.usage.english,
• Purdue University On-line Writing Lab's handouts on Count and Noncount Nouns and Countable and Uncountable Nouns.