Besides taxis, another good way to get from the capital city New Delhi to Jaipur is by bus. This is especially safe for female travellers and those travelling alone. Delhi to Jaipur by bus is over 280 kms and takes about 5 hours, and sometimes more, due to traffic jams.
The main operators of the services are the interstate RSRTC (Rajasthan State Road Transport Corporation) and DTC (Delhi Transport Corporation: http://dtc.nic.in/dt4.htm#5). There are several bus types available - from the ordinary (non A/C) barely-there service to the luxury air-conditioned ones.
The most luxurious bus service currently plying the route is the RSRTC's Volvo Service - a 45-seater spacious air-conditioned (AC) super luxury Volvo bus which also offers on-the-move entertainment by Airtel digital TV (comprising TV screens for every seat). There are many buses running at regular intervals each day and the fare is around Rs 500 per seat. The official website is http://www.rsrtc.gov.in/services.asp, but you can also find useful information regarding timings and ticket prices on http://www.indiatransit.com/india_bus_routes/jaipur-delhi.html