The Tag Block will show a list of tags in two columns, with a hash tag icon besides each tag.
If your site has a large amount of tags and you dont want a huge list filling up your index of your site, you can use one of the alternate tag widgets.
Two other Tag Block Widgets are available.
Popular Tags (being posts with most tags) this list is sorted by count.
Popular Tags and Sorted (this will also list the top tags but it will by sorted in alphabetical order)