Numbers - Signed Integers
This site gives an introduction into signed numbers.
http://www.math.com/school/subject1/practice/S1U1L10/S1U1L10Pract.html

Integers and Signed Numbers Worksheet
Use this site for information on integers, absolute values, comparing integers, and for adding and subtracting integers. This site allows you to create your own worksheets for these topics.
http://www.edhelper.com/integers.htm

Adding Integers
This interactive site is an excellent site in explaining addition.
http://www.mathgoodies.com/lessons/vol5/addition.html

Number Line
This gives some practice using a number line (the site is called "line jumper"). It was designed for kids, but nevertheless is an interesting site.
http://www.funbrain.com/linejump/index.html

Adding and Subtracting Integers
This site gives some practice adding on a number line.
http://www.math.com/ school/subject1/lessons/S1U1L11gl.html