Votes from people (links). How long do you think Facebook stayed in Google's sandbox for? If Google can detect "the masses" flock to any given website, it can be indexed in minutes. Use Social, site incoming links, viral, create buzzes, etc. H
Not to sound stupid, but the best way IMO is to build a site with a lot of content. That is really the first thing anyone who wants a site indexed in google should do. In fact if you do a good enough job with your internal linking system you can do fairly well with niche markets without ever getting a single external back link. Back links are also a given, but unless your site is established or you have good connections with other webmasters you are not going to get quality back links easily. So start with content and work from there.
Submit links to social networks like digg.com, add your sitemap to google webmaster tools, submit articles to article directories.
Create a sitemap and submit it to Google via the Webmaster tools. I've had my site indexed in as little as thirty minutes by doing this.
The sitemap does help indexing, but usually not as quickly or as effectively as simply getting a link from an established site like digg (or even this forum). You can also write up a press release about your site with a link in it and submit it to several press release outlets. They usually only account for temporary traffic, but in this case they are very effective at pointing the google crawlers to your new domain.
You might be interested to read this post telling how to get indexed fast in Google. http://www.dailytechnologytips.com/2008/07/how-to-get-your-website-indexed-fast-in.html
Google likes popular Web sites and ones that match the keywords given. It's important to have META tags that tell Google about your site but nowadays Google can already do that by itself and doesn't rely too much on your META tags. So make sure a ton of other sites link to yours which Google values greatly in placing your site above others in matches and spread the word.