For a long time I felt like a crazy person for constantly closing documents in SSMS just because I could not easily access the documents that no longer had a visible tab. I would find myself resizing Object Explorer, maximizing SSMS, etc. to be able to see all the tabs. I'm sure I'm not the only one. In fact, Sergey Vlasov has created a Visual Studio plugin to deal with exactly this. Since SSMS is built on top of Visual Studio, the plugin works for those that also work exclusively in SSMS.
Visual Studio Gallery Link
Thank you Sergey!