Hartalika Teej (Bhadrapada Shukla Tritiya) is celebrated on the 3rd day (tritiya tithi) of the Bhadrapada month. Lord Shiva and Goddess Paravati (Gauri - Shankar) are worshipped this day. On this day, women keep fast for the long life of their husband similar to Karvachauth. Girls also keep fast on this day for getting a good husband. In this year 2008, Hartalika Teej will be celebrated on 2nd September. It is primarily observed in Rajasthan, Bihar, Jharkhand, Uttar Pradesh, Madhya Pradesh, Chhattisgarh and Maharashtra. In some places, the Vrat is observed for three days but nowadays one day vrat is more common. This ritual is observed as Swarna Gowri Vratam in South India. In Nepal, Hartalika Teej is of great significance and is observed for three days and ends with the Rishi Panchami pooja.
This website talks about Hartalika Teej Vrat and Katha in detail in Hindi. Vrat and Katha can be found in English here.