Vim

# Uppercase
{Visual}U  - Make highlighted text uppercase.
gU{motion} - Make {motion} text uppercase.

# Lowercase
{Visual}u  - Make highlighted text lowercase.
gu{motion} - Make {motion} text lowercase.

# Toggle case
{Visual}~  - Switch case of highlighted text
g~{motion} - Switch case of {motion} text.

# Examples:

gUiw make a word uppercase (i:inner, w:word)
guiw make a word lowercase