Matsumoto-san is another widely-heard voice artist, both in her music recordings and her dubbing work in anime, where she has had lead or supporting roles in dozens of series. She has also had a radio show in Japan and does some dubbing work for translations of American films and TV series into Japanese. You can find out more at Hitoshi Doi's page (which is now a bit dated), Ryuu's Seiyuu Info (which has more of her recent roles), or at her official page, Rica-Net, with sectors in both Japanese (current) and English (last updated in 2000). She is also Anime Personality of the Week for 5 October 2003 at A Fan's View, where you can also find coverage of her appearance at Otakon in 2003. While she is still active in voice acting, her major performance work now is with the group JAM Project, which performs songs for and from anime; one of their famous performances was a 24-hour marathon during which members of the group sang excerpts from one thousand anime songs.
[note: take care on searches not to confuse her name (as I did) with Matsumoto Rika, who is an entirely different person]
Probably Matsumoto-san's biggest acting "gig" to date is as the voice of Satoshi (Ash Ketchum, we calls 'im in the U.S.) in Pokémon; in addition to being a seiyuu, she has also written some of the opening songs (I don't know if we've heard any of them here...).