Junior Jyotish - Free Download. Good for beginners. No time limit.
Jyotish
Tools for Windows - 30 day trial version of this professional
vedic astrology software is available. More features than Junior
Jyotish and good for professional astrologers.
Parashara's Light - I have not used it personally but they claim to be the leader in Vedic Astrology Software. Software available for PC and Palm.
Horoscope Explorer - Generates horoscopes and a wide variety of predictions and reports. Free Evaluation Version can be downloaded.
Muhurta Explorer - Software that determines the best time ( Muhurtha / Muhurta / Muhurat ) to perform events like weddings, journeys, commencing business, house warming etc. Available in English and several Indian Languages. Free Evaluation Version can be downloaded.