For a long time I was looking for a plugin that would work as an info box that made a little box with information that would be visible on all sites/posts at my WordPress blog. I looked and tried lots of plugins but none seemed to meet my need. So I gave up!
Let us say that you have a blog about clothing and you want to have the chance to give information in a special box visible on all your pages when new goods arrive or when some special discounts are available. This is not to be seen as an ad in the sidebar, but in the actual post/page as a sort of information box looking different from the rest of the content. So, yes I gave up and then I started testing plugins for custom text boxes in the blog. I tested a couple and then suddenly one plugin did exactly what I had been looking for earlier, show up on every single page with the text I desired, and with a custom background color I could decide for myself.
The plugin in itself is not very advanced, in fact it is very easy, but it might turn out to be exactly what you are looking for. If you want to try this yourself, search for Stellissimo Text Box among the plugins, and you should find it. Just download, activate and go to the settings for the plugin. This is the way it look and this is how much customization can be done as you use the plugin.
If you have done it correctly it will show up on your site, and if you are lucky it might look something like this. The screenshot was made looking at howtoipaddressin.com on August 1st in 2013, and it shows how it can look if you use this plugin.
Go ahead and try yourself! Feel free to share further knowledge, experiences and thoughts as you write a comment!