The answer is not as easy as there are not as detailed documentation as for other technologies.

Do you search for BigTable documentation or for opensource-alternatives?

HBase is a near-clone of Google’s BigTable.
Cassandra is more a BigTable/Dynamo hybrid.

A nice introduction i can remember was Ricky Ho’s NOSQL Patterns from Nov. 2009 [1].

Of course there is the common overview, you know yet:
- Ian Varley’s master thesis from 08/2009 [2]
- some Cassandra slides from 2009 [3]
- a slideshare presentation on “Key-Value stores: a practical overview” by Marc Seeger (Stuttgart 2009) [4]

Maybe some coding examples [6] help or
stumble through the Casandra homepage [7].

If you prefer learn by doing, have a look on this cool Casandra tutorial of Evan Weaver from Twitter [5].

[1] Ricky Ho’s NOSQL Patterns Nov. 2009
[2] Varlay Master Thesis Aug. 2009
[3] Some Cassandra slides 2009
[4] Key-Value Stores – a practical overview by Marc Seeger 2009
[5] The Cassandra Tuturial by Evan Weaver July 2009

[6] Cassandra Client Examples
[7] Cassandra Getting Started

Hope this help.

Update

I forget to mention this helpful tutorial on database modeling with Casandra
“WTF is a SuperColumn? An Intro to the Cassandra Data Model” [8] by Digg’s Arin Sarkissian.

[8] WTF is a SuperColumn? An Intro to the Cassandra Data Model Sep. 2009