I know it's fairly straightforward to run queries on MongoDB using the terminal. But a GUI tool like PHPMyAdmin (but for Mongo) will be great for day to day development.
While not exactly web based but it is high quality and open source product called Robomongo. It is cross platform and can be used anywhere (Windows/Mac/Linux).
I normally use github.com/andzdroid/mongo-express mongo express. Easy to set up, really fast and it's a charm to use. ;)