While craigslist is one of if not the most popular site right now, clickindia is also very good, there are many classified sites on the net. You want to get your name or items out there, then spread out and the more you use the better results you see. I personally am going to try a new one listed above in this post that I have not used before. I have tried out most of the ones listed in this thread and have had good results for the most part.
For hassle free posting try my classified ads website below, no registration required. Easy three step ad placement.