The Web Nebulae:An overview of nebulae, with color images and links.
Dr. Seth Redfield: Description and visualizations of the Local Interstellar Cloud, a column density calculator for it, and links to popular articles and research papers.
Interstellar Medium Learning pages: About ISM from history of observation to current status of understanding.
Interstellar Molecules evolutionary cycle: Evolutionary cycle of Interstellar Organic Molecules - Fullerenes, PAHs, Polyyenes, and biomolecules.
Nebulae: Part of a larger site on plasma physics.
Observations of Interstellar Molecules: About observation of Interstellar molecules in the ISM and Physical information obtained from them.
The UCL Centre for Cosmic Chemistry and Physics: University College London. Research into the chemistry which occurs throughout the universe in interstellar space.