For something that is often uncharitably termed a dead language, Sanskrit is remarkably alive and vibrant on the internet. Any enthusiast looking to deepen his knowledge of the language, or a beginner seeking to explore and get a grasp of its basics, can avail from dozens of comprehensive learning resources online and even learn through mobile apps.
The best interactive resource for beginners (perhaps even the oldest) is possibly the Sanskrit lessons provided online by Acharya, an institute that is part of IIT-Madras in Chennai, India. These lessons form an easy, step-by-step guide to grasping the basics of conversational Sanskrit. (www.bit.ly/acharya-lessons) The lessons include audio and Flash content, and interactive quizzes to test your knowledge.
Samskrita Bharathi, an organization known in India for its intensive spoken Sanskrit courses and camps, has archived several of their learning documents online and also allows the serious student to sign up for their distance-education program. (www.samskritabharati.org)
For those who prefer audio learning to text, the University of Michigan's Center for South Asian studies has a comprehensive list of audio files from the book "Samskrita-Subodhini: a sanskrit primer"--perfect to listen to in the car. (www.bit.ly/umich-edu-sanskrit)
If video is more your speed, the YouTube channel by user apbshah (www.youtube.com/user/apbshah) has a fantastic series of spoken Sanskrit videos aimed at increasing your conversational ability.
Since learning an Indian language is often easier done through another Indian language, Tamil speakers can avail of the Tamil-to-Sanskrit resources at www.sangatham.com.
While Sanskrit apps have yet to make a significant mark, the iOS and Android app "Sanskrit Primer" is a boon for Sanskrit students. Containing easy reference guides to grammar and terminology, with accompanying audio pronunciation files, this app is a must-have for anyone looking for a convenient pocket reference guide. (See www.sparshapps.com)
There are quite a few active blogs in Sanskrit as well, to add to your daily surfing ritual. We recommend: www.practicalsanskrit.blogspot.com; www.learnsanskrit.wordpress.com; www.samskrtam.wordpress.com; www.slabhyankar.wordpress.com and www.venetiaansell.wordpress.com.
During your study, one wonderful daily resource to help you practice and learn would be the daily news broadcasts in Sanskrit done by All India Radio, available online at their site: www.newsonair.com/nsd_schedule.asp
For those not inclined to dive right in to the study of the language, this PDF lets you share in the joy of Sanskrit's incredible dexterity and the unbelievable sophistication of Sanskrit poetry, possibly unmatched by any other language in the world. See www.bit.ly/roc-sanskrit and download this file: 14339015-The-wonder-that-is-Sanskrit.pdf
We've only touched upon the surface of the various Sanskrit resources available online. If you are interested in further exploration, these websites have comprehensive lists of the wealth of information and resources available online:
Good luck in your efforts, or rather, शुभमस्तु