Some of these portlets are developed by IBM and others are developed by vendors. You can find if the portlet is free or available for fee from Details tab -> Categorization -> Price. You wont be able to find the price from Solution catalog though.
Some of the portlets that i like are
- IBM New SIte Wizard:This portlet can be used to create new portal sites based on template
- Web Application Integrator for IBM WebSphere Portal:THis portlet allows to add portal header on your custom web applications
- IBM Portlet For google gadget: THis portlet allows you to display a google gadget as portlet
- IBM WebSphere Portal Widget portlet:This portlet can display Widget Specification 1.0 compliant widget as a portlet