Typically, a search engine likes to pick up new URLs and pages via a normal web crawl. You can see at Ask.com's Webmasters page (a page that has grown to add more information over time) that Ask.com's crawlers go around the web from link to link, looking for new and important content.
Ask utilizes Web crawlers to collect raw data and gather information that is used in building our ever-expanding search index. Crawling ensures that the information in our results is as up-to-date and relevant as it can possibly be. Our crawlers are well designed and professionally operated, providing an invaluable service that is in accordance with search industry standards.
But in the past, you were able to do paid inclusion, that is no longer available. But as Ask.com says, they do want to find new pages during the normal crawl process.
As a result of some recent enhancements to Ask, we're confident that we're indexing even more Web pages than ever, and that your site should appear in our Search index as a result of our ongoing "crawling" of the Web for new and updated sites and content.
Also in the past you were able to submit your pages to firstname.lastname@example.org or email@example.com to get included. An old 2003 thread from WebmasterWorld claimed that it worked in the past. Does it still work? I hope to find out and update this thread, but I highly doubt it.
Currently, the best way to get included is via nice topical and popular links. Then just be very very patient.
Forum discussion at Search Engine Watch Forums.