They also announced FREE SimpleDB trial for upto 2,000,000 queries per month, every month for next six months.
http://blog.sdbexplorer.com/2008/12/simpledb-2000000-free-requests-for-next-six-months/

What does this mean for Bucket Explorer?

We added “Audit Reports” in Bucket Explorer’s June 2008 release. Not many people have been able to use that since SimpleDB was in private beta. Now since its available to everyone, more Bucket Explorer users can choose the option the create Audit Reports in SimpleDB. This is especially useful for Team Edition, where you may need to track S3 usage by team members with whom you have shared your S3 account.

Another important feature, which our users should expect within next few months is “indexing of S3 meta data in SimpleDB”. This will make Bucket Explorer much more responsive when managing buckets with a large number of objects.