Is there any way to find out where exactly the "Data Transfer" charges in AWS originate from? I'm running a EC2 and a RDS micro instance (Free Tier, both Ireland) + Snapshots and $10 of my $20 bill (not much but still) are "Data transfer" charges.
The detailed billing reports have much more information, although if you're asking "which URLs are consuming the most bandwidth" then the detailed reports won't answer that.
Assuming you serve HTTP, if you what to know which requests are using the most bandwidth then you'll need to analyse your HTTP access logs. Personally I have my HTTP access logs go to CloudWatch logs, then every now and then I run a script that dumps them to S3 and I analyse them in EMR. If you don't have a huge volume of traffic you might be able to make do with just a spreadsheet application.