If you want a REST interface and a GUI then Virgil may be interesting.  I just came across it and haven't tried it myself yet.

On Fri, Mar 30, 2012 at 2:15 PM, John Liberty <libjackjl@gmail.com> wrote:
I made some updates to a cassandra-gui project I found, which seemed to be stuck at version 0.7, and posted to github:  https://github.com/libjack/cassandra-gui 

Besides updating to work with version 1.0+, main improvements I added were to obey validation types, including column metadata, when displaying or accepting data. This includes support for Composite types, both keys and columns.

I often create CF with non string keys, columns, values, and especially Composite types... And I need a tool to browse/verify and then add/edit test data, and this works quite well for me.

John Liberty
(585) 466-4249