The methods described above require a degree of editing before the poetry can be published. Some webmasters may not have that amount of time at their disposal. I don't recommend the following, but I will mention that many editors prefer a quick and dirty method of getting a page of poetry online when it has been received in digital form anyway: simply enclose the plain text of the poem in <pre>...</pre> tags.
A quick survey in March 2002 found a variety of mark-up methods were being employed even within poetry websites, but few appeared to be aware of the benefits of CSS. The Boston Review was in some instances enclosing each verse/line in <p> tags, but elsewhere employing <br> tags. No house style is evident. Of two cantos by Dante, one was indented with crude non-breaking spaces and the other semi-illegally with <dd> tags.
The general method employed at The Atlantic Online, Jacket,
Poetry Daily, Big Bridge and The Blue Moon Review was to group stanzas in <p> tags and turn verse-lines with <br> tags. Plagiarism.com was inconsistent, but most often used the BR method.
The Electronic Text Center at the University of Virginia Library has an online archive of tens of thousands of SGML and XML-encoded electronic texts, but appears to have barely begun to consider modern macro-typographical presentation of those texts. Its current fact-sheet indicates an awareness of the ways that XML could be coupled with CSS to generate a decent display, but actual moves in this direction are not yet visible.
The Electronic Text Center follows standards set by the TEI in its mark-up, but this mark-up is not fully semantic. In a Lewis Carroll example of tagging, the secondary rhymes are marked to "indent" (a description of display only). The pure practice would be to mark out the rhyming scheme as the original Carroll typographer did, and then set a rule whereby the verses/lines indent when appropriate, but the TEI way of marking rhyme schemes is evidently too complex to be practicable. At the University of Toronto English Library, tagging is also limited to a primitive TEI scheme.
It bears mentioning that some poetry evades all mark-up and description by SGML schemes because the poet's macro-typographical requirements are too eccentric. Concrete poetry, for example, is best represented by image files. And the Calligrames of Guillaume Appolinaire (1880-1918) provide an even more extreme example of the limits of mark-up language.
For some excellent thoughts on the preparation of poetry manuscripts, see the John Tranter's style guide for the Australian online literary magazine Jacket. His conclusions are not in agreement with those on this website, but are to be respected.