It takes a while for domains to propagate, is it a new domain? Have you developed any off site links? Have you pinged any services about your site's content? Do you have any RSS feeds, blog or anything else? Have you done any SPAM? There can be 1001 different reasons it can take a while for google to list you. Do a search for your domain name itself once a day, build links, read google's webmaster guidelines and stay away from black hat stuff!
Some search engines, notably Google, may not even bother to visit your website to index it. Other common reasons may be- 1. Low or no links from your site. 2. A Web 2.0 Website Without Traditional Web Content and Navigation: New is Not Necessarily Better 3. More Pictures Than Words: Even A Few Words is Worth More Than a Picture.(Your site is not opening for me...) May be you are having poor hosting service.