I heard Sanskrit is pretty difficult to master, but I found lots of online resources.
Complete Books (PDF format):
A Practical Sanskrit Introductory (PDF: 156 pages)
Free to download from URL.
Introduction to Sanskrit (2 Volumes)
Online tutorials:
Learn Sanskrit Online
Focuses thoroughly on grammar
Learn Sanskrit Through Self Study
12 Introductory lessons. Focuses on common phrases and everyday expressions.
Ukindia: Sanskrit Lessons
The Hindi Lessons Component (should be done first to know how to read the script)
Learning Sanskrit In Distance Learning Mode
Very comprehensive Blog
Sanskrit Step By Step
Offers lessons for every month with exercises and answers.
Sanskrit Pradippika
Downloadable software that teaches Sanskrit. Haven't tried it yet. Tt's free.
Misc
Learn Sanskrit through Hindi
Teaches how to learn to write Sanskrit: a shortcut through Hindi
How To Write Sanskrit
Sanskrit Applet
Shows animation on how to write each character
Resources
Sanskrit Resources
Offers a set of resources for Sanskrit, including dictionaries, tutorials and applications.
Sanskrit Studies Links and Information
A huge directory of links and information related to Sanskrit.
Sanskrit Language Texts
UBC Site, with texbook suggestions for learning about Sanskrit
Speaking Sanskrit.org
Seeks to promote the speaking and writing of Sanskrit
