{{nowrap}} prevents wrapping within a single template (i.e. not suitable for relatively complex or lengthy content).
{{Nowraplinks}}...{{Nowraplinks end}} prevents wraps inside links while allowing wraps between links and in normal text. Very useful for link lists and easy to use.
{{Nowrap begin}}...{{Nowrap end}} prevents wraps in both text and links. For the trickier wrapping cases when you need full control, for instance in very complex link lists.
{{Spaces}} to produce multiple non-breaking spaces (or a single one).
{{Inline block}} affects, but does not entirely prevent, line wrapping.
{{wrap}} can be used to provide a (brief) exception within a no-wrapping area.
{{Normalwraplink}} allows links to wrap when they otherwise would not.
In particular, to avoid line wrapping when quoting a passage such as a poem or computer code, see {{Quote#Line breaks}} - e.g. Template:Blockquote with "poem" tag.