this anime I'm almost finished w/ this anime (in Japanese, but I did it chronologically). I seen on wikipedia, and here, that an American co dubbed this show. By the look of it, almost all the VA's are pretty good. Heres the list if you don't know about it:
Haruhi Suzumiya: Wendee Lee- shes pretty well know, very experienced and very well known for her role in Cowboy Bebop as Faye Valentine, TK in Digimon, Dorothy in MAR, and Yahiko in Rurouni Kenshin.
Kyon: Krispin Freeman, he's also well known, but mostly for the rople in Blood+ as Haji, Holland in Eureka 7, Alucard in Hellsing, some people in Naruto in cluding Itachi, Tsume in Wolfs Rain and Wonrei in Zatch Bell. He was also in Final Fantasy 7, the movie
Yuki Nagato: Michelle Ruff, which is Rukia in Bleach, Alvis in Last Exile, Snow in MAR, Elie in Rave Master, and some various people in Zatch Bell
Mikuru: Stephanie Sheh, which is Orihime in Bleach, Eureka in Eureka 7, Hinata in Naruto, Mamimiin FLCLand Penny in Zatch Bell
Last and not least Koizumi, which is voiced by Johnny Yong Bosch (which I'm sure you know already, so no need to say about him)