Histograms
You can look at the influence of bin width on   a histogram with this neat applet
You can look at other data set histograms and play with them on a related site.
Check out a tutorial on histograms, stem and leaf diagrams and other tools (e.g. box plots) in this chapter
Or do a histogram with your own data

Stem and leaf diagrams
lots of ins and out of how to do it

Pareto charts
An example, some history and definition

Scatterplots
Interactive scatterplot drawer based on census and other data sets

Pie charts (pass a slice, please; or better yet, pass altogether)
You don't need a recipe for this pie chart maker, use it to do your homework

General data visualization
Gallery of data visualization - the stars and the duds. Contains a great boxplot example showing what these can be at  their best.