The Speculative Evolution Wiki
If you need some guidance in creating scientifically accurate and plausible habitats and organisms for your exobiology project, the Speculative Evolution Wiki is a great resource to start with. There is a page on the types of alien planets thought to exist. There is a page on alternative biochemistries. There are pages covering the wide variety of approaches Earth life takes to common problems, such as movement, perception, reproduction, defense, and the various ways that an organism might draw energy from its environment.
The Conceptual Evolution Forum
The Conceptual Evolution Forum is where you can connect with other speccers, posting about your own projects and commenting on others. Get feedback on aesthetics and scientific plausibility from thousands of people all over the world. There are different sections to discuss future evolution on Earth, what might have happened on Earth had evolution run differently, other planets, and other universes where the laws of physics are different. Register and say hello.
Podcasts by B. E. Kern
If you are a world builder who needs to ground your life form designs in scientific plausibility, the podcasts at BEKernWrites.com are a good place to start. Each runs about forty minutes long. Subjects such as biomes, metamorphosis, metabolism, and genetic material are covered by an actual professor of biology. The lectures stick pretty close to describing Earth life most of the time while briefly mentioning some of the variations found across the galaxy. It is not wildly speculative.
Spore is a computer game of five levels. First, the player creates a unique aquatic microbe that must survive the hardships of nature. Continual tweaks can help it to better thrive in its environment. Next, it becomes a land-based creature. Next, it develops social groups. Next, it develops technology. Finally, it colonizes space and this level is played against other empire-builders online.