\makeatletter \let\@texttop\relax \makeatother
in the preamble of your file.
Doing-it-yourself is a common strategy; Knuth (for use with Plain TeX, in the TeXbook), and Kopka and Daly (in their Guide to LaTeX) offer worked examples. (The latest version of Knuth’s macros appear in his “local library” dump on the archive, which is updated in parallel with new versions of TeX — so not very often…) Nevertheless, there are contributed alternatives — in fact there are an awfully large number of them: the following list, of necessity, makes but a small selection. The largest, most comprehensive, class is newlfm; thelfm
part of the name implies that the class can create letters, faxes and
memoranda. The documentation is voluminous, and the package seems
very flexible.
Other classes recommended for inclusion in this FAQ are
akletter and isodoc.
The dinbrief class, while recommended, is only documented in
German.
There are letter classes in each of the excellent
KOMA-script (scrlttr2: documentation is available in
English) and ntgclass (brief: documentation in Dutch
only) bundles. While these are probably good (since the bundles
themselves inspire trust) they’ve not been specifically recommended by
any users.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=letterclass