A lot of people have asked if the Slake stories are a series. The concise, authoritative answer from the author is: Not really. But they are set in the same world. Andy (from Alphabet Soup) is a minor character in A Russian Bear, but you don't have to read A Russian Bear to read Alphabet Soup or vice versa. Even though it would be lovely if you did. I do recommend that you read Alphabet Soup before reading the short story I Like You, though - it'll make more sense that way.
Oh, and the two Himiko books are simply one story which got too long to fit a single book. Don't say I didn't warn you!

Slake stories:
Who You Are (free story)
A Russian Bear
Alphabet Soup
Malaria, Cholera, and Bubonic Plague (free story)
I Like You
Saturday Night, Live (free story)
Of Russian Myth and Lore

Himiko:
Himiko: Bonding (part one of the series)
Himiko: Warrior (part two of the series)

Standalones:
Knowing it by Hart
Going Home (out of print)