Gulp-connect is capable of starting a small web server on your local machine. This is nice for development and testing. Once you couple it with live reload and watcher tasks, you can trigger page reload every time you update things.
This is a complement to gulp-connect and allows you to use rewrite rules, much in the same way you'd use them with apache's mod-rewrite. I use it to make gulp-connect serve local JSON files mocking the real production layout and I got the idea from here.
This plugin allows you to create tasks capable of monitoring file changes. You can use it for e.g. continuous builds, in conjunction with server plugins etc.
Gulp-if is a nice plugin allowing you to execute a particular function when a condition is true. I use it now to define conditional behaviour for development vs. production (e.g. "don't minify stuff in development").
As a side note, there's a gulp-if-else plugin as well.