MarkdownPad is a free Markdown editor for Windows that that can convert Text to HTML or XHTML for you easily. Dwnload the free version here.

It may not be exactly what you are looking for, but I use this service to convert my blog entries from text to html.<BR><BR>It allows you to use a convinient shorthand, such as _italics_, *bold ...

This OPML to HTML bookmark converter makes an HTML bookmark file (with browser-friendly, clickable links) from OPML you submit to it.

Convert files to multiple formats: This is the primary feature of this software. You can convert one file into multiple text formats within moments. It supports PDF, HTML, RTF, DOCX, etc.

Converting texts between formats is a bit of a pain to do on a file-by-file basis, but thankfully, MacIssues shows how to convert text files in bulk using a simple terminal command.