Yui Makino is my personal favorite. She voiced Sakura (Tsubasa Chronicles) and more recently Yura (Stella Jogakuin C3 Club) but is much more famous for being an ultimate boss at singing, her most well-known piece being Undine (Aria the Animation OP). Her voice is the sweetest thing I have ever heard.
Seconding that. While she isn't my personal favorite, my personal favorite would require you to watch whole series to be convinced of what she can do; so it isn't easy to promote her. Whereas Makino Yui's impressive point is her voice herself. So hearing her in her role of Sakura for example, or hearing songs likeUndine
, yume no tsubasa
should be enough to promote her.
Miyuki Sawashiro - Yomi (Black Rock Shooter), Canaan (Canaan), Himeko (Kokoro Connect), Fujiko (Lupin III), Shinku (Rozen Maiden), Perrine (Strike Witches), Nanami (Prince-sama).
Another good choice here. Hearing her as Himeko in kokoro Connect should be convincing enough ImO. Talented Seiyuu here, who has both a great variety in her role as well as the skill to perform complicated roles.
Although, my favorite to recommend would still be Orikasa Fumiko. This is a seiyuu that you'll probably won't notice that much (although her voice is quite good and cute in itself) as long as you give her plain roles to perform. But give her roles when she needs to carry a lot of emotion in her voice, roles where she needs to often switch from a tone to another, from an emotion to another, from a speech pattern to another, and you'll see her shining. Her performance in roles such as pacifica cassul (scrapped princess) or Rukia (Bleach), Victoria Seras (Helsing/Helsing Ultimate) are good example of what she can do. She has an extremely large range in her doubling, as she has done almost every type of girl you could think of; from the sweet and reserved girl like Chise from Saikano or Kirara from Samurai 7, the girl full of energy like pacifica, the cool beauty like Riza Haweye from Full Metal Alchemist, the friendly and loving girl like Shirley from Code Geass, the tsundere type like Meia Gisborn from Vandread, the teacher type like prof. fuyutsuki from GTO ; her range is so great that it's usually quite difficult to recognize some of her performance as being from her.
She usually fit very well the role no matter what it is. Most of the famous seiyuu are easily recognized even when they do plain role; I actually think that this isn't a proof of skill as when you hear the voice you actually think of the seiyuu rather than the character voiced. Whereas in Orikasa Fumiko's case, you properly associate her character doubled with her performance rather than with her, and this is how it should be.
Which is why she may be difficult to recognize, and will be remembered more often when the role is complicated.