A reader for big HTML files and/or zipped HTML bundles?
You could try using the default Android browser.  Open the browser, in the address bar enter: file://sdcard/file.html (replace the part after sdcard/ with whatever path leads to your file).  You can then bookmark the file and open it later in the browser without having to re-type the address.  However, trying to make a "bookmark shortcut" or using the HTC bookmark widget will not work for local files.