An excellent free program is available at:
This program transliterates between Sanskrit and English either way
(example from the Isha Upanishad)
The page has links to other excellent sites for Sanskrit texts, software and learning materials
Below is an Acrobat PDF file of the Vivekacudamani (Crest Jewel of Wisdom) of Shankara with the Sanskrit text and English translation of each verse
Crest Jewel of Wisdom
Note: This is a long text and you might prefer to download it rather than read it on line
Here are a selection of Sanskrit only texts in PDF files
More Sanskrit texts will be added as I make them.
Note: you need the free Acrobat Reader to read these files. This program can be downloaded by doing a web search for "adobe acrobat reader". With Acrobat Reader installed no extra fonts are required. You can then print the texts in Sanskrit to any size paper.