Please, specify
Hi,
What developers do you refer to? There are lots of emulators, and lots of developers behind them. You can support them in many ways. You can donate for some projects like Project 64 to partially support the development. Others projects don't accept donations, but there is always a few things to do to thanks the authors.
You can even involve yourself in a project if you are interested in emulation. Not only coders are requested for emulation projects. Beta testers, designers, webmasters and so are usally wellcome. Suggestions in the forums about how to improve a certain emulator, bugs founds and so also helps.
Feel free to ask whenever you want to.