What is there to say about them?
Most formatting tags have been deprecated (which means they are expected to become obsolete) in HTML 4.0. They have been replaced by Cascading Style Sheets.
Since Cascading Style Sheets are so much work, and since browsers still support them, I still use the ones that are fully or widely supported and stay away from the others.

1. <address> (to set apart an address)
2. <b> (bold)
3. <big> (increases font one size)
4. <blink> (even though it drives me crazy)
5. <br> (add blank lines and space)
6. <center> (now I use div)
7. <cite> (for a reference)
8. <code> (computer code)
9. <dd> (definition list description)
10. <div> (alignment or CSS)
11. <dl> (definition list)
12. <dt> (definition list term)
13. <em> (emphasis - rarely)
14. <font> (font face, size, or color)
15. <i> (italics)
16. <kbd> (command line stuff)
17. <li> (list item)
18. <nobr> (keep stuff together)
19. <ol> (numbered list)
20. <p> (paragraph spaceing)
21. <pre> (screen or printer output, etc.)
22. <small> (decreases font one size)
23. <strong> (strong emphasis)
24. <sub> (formulas, etc.)
25. <sup> (formulas, dates, etc.)
26. <tt> (typewriter stuff)
27. <ul> (unnumbered lists)
28. <var> (variable names)
29. <wbr> (suggested line break points)

1. <abbr> (abbreviations)
2. <acronym> (acronyms)
3. <basefont> (set the base font for the page)
4. <blockquote> (large block of quoted text)
5. <del> (deleted text)
6. <dfn> (definition)
7. <dir> (directory listing)
8. <inlineinput> (???)
9. <ins> (inserted text)
10. <listing> (text listing)
11. <menu> (menu listing)
12. <plaintext> (plaintext - html ignored)
13. <q> (quotation)
14. <samp> (sample code)
15. <spell> (???)
16. <strike> (strike-out text)
17. <u> (Because it is confused with links)
18. <xmp> (example text)