Armstrong, an undrafted free agent out of college, spent the 2008 season on the Dolphins' practice squad. He had 44 catches for 871 yards for the Washington Redskins in 2010 and made seven receptions for them last season.
The Dolphins hope Armstrong will upgrade a receiving group that was lackluster during the exhibition season.
Nolan made three starts each of the past two seasons for the Houston Texans and had three interceptions as a rookie. Stanford, who becomes the fourth cornerback on the Dolphins' roster, played in 12 games as a reserve last season with the Carolina Panthers.
Brown, an undrafted free agent, spent training camp with the St. Louis Rams.
Culver is a sixth-year pro who started four games for Miami last season. Slaton rushed for 1,282 yards for Houston as a rookie in 2008, but carried only 24 times last season for the Texans and Dolphins.