I use "__Archive" (double underscore) for those tables.
I also maintain its structure to match the original table. That is, if the main table changes, I make the same changes in the archive table. Basically, I want a SELECT * UNION ALL between the two tables to always work.
SQL DBA,SQL Server MVP(07, 08, 09) A socialist is someone who will give you the shirt off *someone else's* back.