9 GPS modules:
While many cameras today have GPS built in, many do not. Camera makers accommodate geotaggers with add-on accessory units, most fitting into the hot shoe. Useful not only for recording the places of your photographs, but for organizing—you can sort by place without having to keyword the pictures.
10 Viewfinder magnifiers:
If you’re finicky about manual focusing, do a lot of macro work, or just plain want an enlarged view through the finder, eyepiece magnifiers are a nice accessory. We prefer types like the Nikon DG-2, which flips up and out of the way via its hinged mount.
11 Viewfinder screens:
A fair number of DSLRs have focusing screens that can be interchanged by the user. A number of these screens are designed to provide easier manual focusing, so if you have manual-focus lenses, or are into DSLR video, you might check if an appropriate screen is available.
12 Wi-Fi and Bluetooth connectivity modules:
If you’re big on photo sharing, connectivity modules such as Olympus’ Bluetooth PenPal for Pen ILCs are a neat solution. With this, you can upload photos to your smartphone automatically.