Create your own social bookmarking site.
Add Reddit-like voting functionality to WordPress posts and comments.
Order comments/pages based on what’s trending or use standard criteria like title, post date, etc. You can also order pages based on their page rating (the percentage of upvotes out of total votes cast).
W3 Votify works perfectly with with cached web pages (so pages don’t need to be regenerated/refreshed whenever a new vote is cast).
You can modify your theme to use Votify with your comments or you can use W3 Ajax Comments (with Votify support built in).