One problem in answering this question is that there is no
one authority as to what constitutes a legitimate word. Ross
Eckler's "Making the Alphabet Dance" lists 24 anagrams
of the letters 'aest', but many of these are quite obscure and
they are drawn from a wide range of sources.
Merriam-Webster's unabridged dictionary contains entries for
these 14 words:
anestri, asterin, eranist, nastier, ratines, resiant, restain,
retains, retinas, retsina, sainter, stainer, starnie, stearin.
Other wordplay sources omit some of these words and/or add
others, including the multi-word anagrams 'tin ears' and 'in
Word Ways has for some years been collecting anagrams of 'aeginrst'.
William Tunstall-Pedoe indicates that a whopping 157 of these
have some justification.
[Source: alt.anagrams FAQ
by Anna Shefl]