Some years ago I gave a talk to the local ancient coin club in which I presented info on websites for research and purchasing. I divided the presentation into sections: General Research, Greek, Roman, Byzantine, Nonclassical, Judaean, English (Hammered), Forgeries and Counterfeits, Noteworthy University and Museum Sites, Noteworthy Retail Sites, Noteworthy Antiquity Dealers, Noteworthy Organizations, and Noteworthy Blogs.
Here are the sites that I believe are still online from the Roman section:
http://www.romancoins.info/Lots of information about Roman coins, Roman sculpture, and the Roman military.
http://andrewmccabe.ancients.info/Research.htmlAndrew McCabe's site for research into ancient Roman coins. Much info for Roman lovers here.
http://andrewmccabe.ancients.info/I...tml#CampaniaRoman Republican coins and books...great resource if this is what you're into.
http://www.tesorillo.com/aes/home.htmGreat site for help with attributing Late Roman coins (317 - 498 AD).
http://www.coinscatalog.com"...extensive free online reference of Ancient Roman coins. The catalog incorporates a sophisticated search engine for easy coin identification, as well as detailed information and images of the various coins." Also includes a discussion board devoted to the topic of ancient Roman coins.
http://augustuscoins.com/ed/ricix/index.htmlNice site devoted to late Roman bronze coins.
http://home.eckerd.edu/~oberhot/campgate.htmSite with information about Roman campgate coins, as well as Carolingian gate coins.
http://citygate.ancients.info/As the name suggests, ancient coins with city gate motifs. Lots of great pics.
http://www.chicagocoinclub.org/proj.../PiN/rc.htmlIllustrated article by David Sear, explaining the history of Roman coinage.
http://bpmurphy.ancients.info/sever...eranhome.htmBarry Murphy's collection of Severan Denarii. Great pics.
http://tomross.ancients.info/Focuses on the coins of Aurelian.
http://www.ettuantiquities.com/Philip_1/index.htmFocuses on Philip I (and family) antoninianii.
http://www.coinsofromanegypt.org/Coins of Roman Egypt. Well organized research site with good pics and a number articles posted.
http://rpc.ashmus.ox.ac.uk/A site to help you in your research of Roman Provincial coins.
http://gordianiiirpc.ancients.info/Gordian III and Roman Provincial coinage.
http://www.diadumenian.com/Yet another site devoted to Roman Provincials.
http://www.provincial-romans.com/Yet ANOTHER site on Roman Provincials.
http://kevinscoins.ancients.info/The "humble" collection of "Kevin"...a collector's personal site, with galleries of his coins (focusing on Roman Imperial), tips on cleaning coins, and info about bronze disease.
http://www.chijanofuji.com/Roman_Coins.htmlJan de Veen's really nice collection of Romans.great pics.