For high quality Early Imperial Romans (EIR), I would recommend two sources in particular. The best source in my opinion is Corvus Belli Miniatures by Fernando Liste of Spain. Closer to the standard 15mm scale, the Corvus Belli EIR figures feature an extensive range with considerable variety in poses, as well as fantastic detail. See: http://www.corvusbelli.com

AB Miniatures offers a limited range of Early Imperials (circa 19 AD) carved by Anthony Barton. These were originally commissioned for a German museum display and are highly detailed but fairly static poses. They are on the larger end of the 15mm scale and will not mix well with other makers. AB's Early Imperials are available from AB Figures in the U.K. (see: http://www.ab-figures.demon.co.uk) or from Eureka Miniatures in Australia (see: http://www.eure kamin.com.au/), who also produce Barton's outstanding Sassanid and Ancient Greek ranges.

Testudo and Pass o' the North also offer sharp looking Roman figures. Their ranges cover the late Republican period (i.e. legionaries in chain mail), which also works in the Early Imperial period prior to widespread adoption of the Lorica Segmenta or banded armor. Testudo offers the option of cast-on shield designs.

Essex, Chariot, Freikorps, Old Glory, Irregular, Museum, Navigator and others sell 15mm Early Imperials, and all have their adherents. My own EIR army for DBA is mostly Essex and they are good solid figures, although lacking in pose variety. But Corvus Belli is at the top of the heap IMO. For links to these and other miniature manufacturers and retailers, see the Fanaticus Bazaar at fanaticus.org/DBA/Bazaar/minisources.html