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Some Pay For Inclusion (PFI) directories like Inktomi promise to recrawl every 48 hours, however my experience has been that it is more like every 96 hours lately. Check the Pay for Spidering Engines [webmasterworld.com] forum for more info.
i have seen many companies that provide this service..
I've seen a couple of sites which imply that they have some technique for making sure your site is added within 48 hours and re-spidered that frequently. All that they're doing is avoiding saying directly that they use Inktomi's paid spidering program -- which, as is further obfuscated, would mean that you'd be "refreshed" regularly at only a small subset of the search engines that they talk about on the rest of the site.
But short of that approach -- paying certain certain search engines for the service -- there's nothing you can do to increase the rate at which your site is spidered, other than, as has been mentioned, if you are making regular updates to your site there's a chance Google will discover that and pick you up in their "fresh crawl."