Religion or spirituality without sound philosophy usually leads to sentiment or fanaticism. Therefore it is important to understand the process of self realization. Here are some links to the philosophy behind bhakti.
A site I keep up to date with my latest animation videos exploring concepts in Bhakti
A contemporary magazine style site with articles commenting on issues of the day, both within the Gaudiya community and the world at large. They also focus on news articles relevant to the greater spiritual community and the importance of sustainable living. Great for those who like to think deeply about the philosophy and its applications in the modern world.
3. Krishna path
A great site for free book downloads, especially if you use a Kindle or similar e-book reader. I recommend at least reading these books (in this order): Sri Isopanisad, Bhagavad-gītā, Śrīmad-Bhāgavatam, Śrī Caitanya-caritāmṛta.
A great Youtube channel for those who prefer to listen than read. Contains hundreds of videos of book narrations, spiritual lectures and more.