I've already written about this one at length, but I figured I'd include it here anyway for reference and comparison. It's the original awesome CRT shader written by cgwg with some help from Themaister and DOLLS[!], and it's still a good choice. It has extensive customization available via code modification and/or RetroArch's runtime shader parameters.
This one was written by a fellow from the NeoGAF forums who goes by the name Easymode. It is notable for looking nice even at non-integer scale factors and for being very lightweight considering how nice it looks. It's a good one to try on mobile platforms and desktops/laptops with weaker GPUs. It also has some nice runtime parameters for switching between cgwg-style and Lottes-style mask effects.
This one is written by Hyllian, who is well-known for his popular upscaling interpolation algorithm known as xBR. It includes some interesting options, such as a "blue boost" that is helpful for making water in many games go from purple to blue.
This one was written by Timothy Lottes, an engineer at Nvidia who is known for his work creating the FXAA fullscreen antialiasing GPU algorithm. This shader is adapted from the shadertoy he made and was generous enough to release into the public domain. Notably, it uses a sideways shadow mask effect that is designed to avoid chromatic aberration.
This is one I worked on awhile back and it only focuses on doing a phosphor/shadow mask using an external lookup texture (LUT) and a little bit of horizontal blurring.
I've raved about this shader--which was written by aliaspider--before for its ability to blur out dithering, but it also belongs on any list of good CRT shaders. While it doesn't provide any phosphor/shadow mask effects, it does allow horizontal/vertical bandwidth control (for blending things like pseudo transparency and dithering), scanline effects and NTSC color blending/bleeding.
All of these effects are user-customizeable by editing the code (he put the various options right at the tops of the files for easy access) and, with the NTSC color option disabled, it looks remarkably close to the output of Micomsoft's famed XRGB-Mini Framemeister deinterlacing/upscaling device.
This shader is available in Cg and Quark formats.
This shader was written by a guy named TroggleMonkey and it uses some intense, RetroArch-specific black magic to overcome many of the issues with CRT emulation that I thought were unavoidable, particularly using large-scale blurring passes without totally wrecking performance and making a true RGB phosphor / shadow mask that looks good at less than 4K resolution. As I said, it is Cg-only and only works on RetroArch, at that (i.e., no OpenEmu, even though it supports Cg in general).
Written by Themaister, this one eschews phosphor/shadow mask effects and just focuses on using special blurs to accentuate the variable beam width of a CRT (i.e., brighter pixels bleed further into the space between scanlines).
Just like regular CRT-Hyllian, but with some whole-screen blur/glow.
Mr. Lottes made a revision to his scanline shadertoy that added a number of gaussian blur kernels to bloom out bright pixels, which increases the overall brightness of the image without getting the fullscreen haze of some of the other options.
Unfortunately, the limitations of the shadertoy format forced the blurs into a single pass, which is extremely slow. This variant is available in Cg format only.
For anyone who's curious, I took 4K screenshots of most of these, but blogspot down-rezzes them and adds jpeg compression on top of that, so I couldn't post those directly. Instead, here is a download.