Sometimes is useful for trouble shooting (or backup - there will be a separate blog post about that soon) to see all cells including deleted cells and the tombstone markers.
HBASE-4536 introduces "raw" Scans (only available in HBase trunk - not the upcoming 0.92). In the Java client these are enabled by Scan.setRaw(true).
The HBase shell also supports this by adding RAW=>true to a scan.
Once raw mode is enabled the returned result contains not only the standard KeyValues, but also KeyValues for deleted cells and for tombstone markers (which are just special types of KeyValues, more on delete markers can be found here).
Here's an example of what it would look like in the shell:
In this the above example values 'v2' and 'v1' for row key 'r1' have been deleted with a column delete marker.