What are the commonly used block types? What is the special in core/text_list block type.

Commonly used block types: core/template, page/html, page/html_head, page/html_header, page/template_links, core/text_list, page/html_wrapper, page/html_breadcrumbs, page/html_footer, core/messages, page/switch.
Some blocks like content, left, right etc. are of type core/text_list. When these blocks are rendered, all their child blocks are rendered automatically without the need to call getChildHtml() method.