Runners up to DSM?
Winston-Salem, North Carolina (metro: 468,000 but CSA includes Greensboro)

(Chuck Johnson, Flickr)

(Missannies.com)

(City of Winston-Salem)
Lexington, Kentucky (metro: 453,000 MSA but CSA is over 600k)

(hyattregencyphiladelphia.com ?!)

(city-data.com)
Mobile, Alabama (metro: 406,000)
Has a taller building but not the density of Des Moines' skyline

(Wordpress)

(destination360.com)
Little Rock would definitely be on a <700k list (675,000 MSA)