Most of the clustering talk I hear in relation to Linux is about Beowulf clustering. You might have a look at their site:
An older link I have that seems to have discussion of other things is the Linux Clustering site at:
Here we do clustering with Oracle RAC (Real Application Cluster) which includes Oracle CRS (Oracle Cluster Ready Services). This uses OCFS (Oracle Cluster Filesystem) which is available for download from Oracle even if you're not using RAC or CRS. OCFS allows you to have shared storage (mainly for database purposes).
It would depend a lot on what the purpose of your cluster is.