Update (11/08/2012): New shaders added to the end of the post.
In addition to XML/GLSL pixel shaders, SSNES also supports pixel shaders written in Nvidia's proprietary Cg shader language, which is similar in syntax to Microsoft's HLSL language. While Cg hasn't been a very popular language for shaders, historically, many new shaders have been written for use with PS3 homebrew, where Cg is the only supported shader language. In fact, these shaders were downloaded from TwinAphex's SNES9x Next source code repository.
Another benefit to the Cg shaders is that they work with both OpenGL and Direct3D drivers in SSNES, which makes many of the more modern shaders to available to people with poor OpenGL performance for the first time.
As with my previous shader posts, these images were captured at a 3x scale factor, then enlarged using nearest neighbor to 400% for the detail shot. Click the thumbnails to embiggen.
This shader combines Hyllian's 5xBR algorithm with the phosphor-derived scanline shader from Caligari with great results. This shader is designed for use with square, non-aspect-corrected pixels, so be sure to use an 8:7 aspect ratio on SNES to avoid any nasty artifacting. It also expects at least a 5x scale factor, which looks like this:
Here are a few more pictures from the GBA version of Final Fantasy 6 and Street Fighter 3: Third Strike on FBA:
I find the scanlines make text easier to read than with 5xBR alone, for whatever reason.
Download the xBR pack from Hyllian here.
This shader accentuates the individual pixels by adding a cool, beveled look along with some color-tweaking mojo to give them a feeling of depth. Again, it expects non-aspect-corrected images, or else subpixel aliasing effects will make a mess of things.
Here's another picture at 20x (5x scale factor, enlarged 4x with nearest neighbor; see it full size to get the full effect):
Notable ports from the XML shader family include cgwg's CRT shader, Themaister's dot-n-bloom (listed as 'dots.cg') and Waterpaint shaders and an extremely fast implementation of bicubic filtering (bicubic-fast.cg) from Hyllian, as well as all the classics, such as HQ2x, SuperEagle and so on.
Hyllian has been working on some interesting shaders lately, including an implementation of Christoph Feck's "reverse anti-aliasing" algorithm, which allows for some very sharp, smooth upscaling. It works on any image but really shines on digitized images with lots of gradients (think: SNES games with digitized sprites or games with prerendered backgrounds, like Resident Evil or Final Fantasy 7). It's also particularly good at rendering legible text, so it's great for RPGs, as well. Here are some images of this shader paired with some scanlines:
As with pretty much everything else, bsnes has taken some sophisticated steps to achieve an authentic gamma ramp that reflects the actual appearance of games. Themaister was kind enough to reproduce the relevant code in Cg form. This is how it looks:
A simple, fast scanline shader from Gigaherz, LCD3x is intended to evoke the look of handheld console LCD displays:
I'll add more shaders and more pics in the near future.