When I'm searching on Packagist, I try to avoid packages that depend on frameworks that are not Laravel or sometimes Symphony. Of course, no framework dependencies is okay.
When L4 was still in alpha, I wanted to play around with image manipulation. After some investigation, I chose sybio/image-workshop. At the time, there were no packages that interfaced with Laravel perfectly. After created a service provider and facade, all was good.
On packagist.org, try the search terms "mongodb AND laravel" without quotes. This narrows the search to one page, in this case.
Chris Fidao (@fideloper) tweeted on May 2nd about the following MongoDB package for Laravel. It looks interesting as it uses Eloquent.