Workflow Engines for MS Sharepoint

A quick collection:

K2.NET Enterprise Workflow: http://www.k2workflow.com/solutions/collaboration/sharepoint.aspx
Ultimus: http://www.ultimus.com/index
Captaris Teamplate: http://www.teamplate.com/internal/product/sharepointworkflowwizard.asp
Nintext Smartlibrary: http://www.nintex.com/Product-SmartLibrary.aspx
LMR Solutions: http://www.lmrsolutions.com/products_workflow.asp
Skelta Workflow.NET: http://www.skelta.com/

Some more Business Process Management Vendors:
- Metastorm e-Work
- FileNet's Business Process Manager
- Tibco Staffware Process Suite
- Ascentn AgilePoint BPMS

Product Comparison:
http://answers.google.com/answers/threadview?id=357095