Data visualizations are a vital component of a data analysis, they summarize large amounts of data in graphical format which is really important when you are reviewing and comparing many numbers. Some of these charts to compare numbers in visualization are bar chart, mulit-set bar charts, line graph, stacked area graph, bubble chart, etc. This article below about how to chose the right data visualization for your information provides great points and facts about different chart visuals.
This image below is a back to back bar graph that compares a few sets of data numbers and separates it into two graphs that lets you see all the information on one graph. I enjoyed this graph and I think it really helps when you are comparing numbers in data.