Store sflow data in MongoDB. Use it to get your top URLs or Memcache keys. There are currently no Open Source tools that do this yet AFAIK, so I decided to start writing one.
I recommend using the latest dev branch of Mongo because I think the new aggregation framework would be a good fit for counting.
This is just some code I've been playing around with as I practice Ruby and learn about MongoDB. Comments/suggestions/contributions are surely welcome.