The plugin I am going to cover in this post, is an existing one which has been brought up to coding standards; Tag Cloud.
The Tag Cloud plugin creates a configurable widget where tags can be included or excluded from from the tag cloud. Formatting of the widget is also available.
On a multisite, this plugin can be configured at the network level and then these settings used on each site, or site settings then set.
This site uses the Tag Cloud widget in the sidebar.
The plugin can be downloaded via my Development site.