Lawrence Hall of Science
The Math Page: An Approach to Calculus: Limits
Here is a site that clearly and thoroughly explains the concept of limits, including one-side limits, the limit of a function, and the definition of limit. There are example problems solved, problems for the student to attempt, and...
Mathematics Archives
Math Archives: Visual Calculus: One Sided Limits
This calculus tutorial features an explanation of one-sided (left- and right-hand) limits.