I really like the Samalla kartalla book series. You can already get Samalla kartalla 1 and Samalla kartalla 2, and the third one is coming in August. I like to recommend these books for my intermediate students who already know the basic grammar and want to practice reading comprehension, structures and vocabulary. If you want to study really difficult Finnish, check out Finnish for translators.
Here's a post about more material to teach yourself Finnish.