Press ctl-k, then press one of these characters:
Character Meaning -------------------------------- ! Grave ' Acute accent > Circumflex accent ? Tilde - Macron ( Breve . Dot above : Diaeresis , Cedilla _ Underline / Stroke " Double acute (Hungarumlaut) ; Ogonek < Caron 0 Ring above 2 Hook 9 Horn = Cyrillic * Greek % Greek/Cyrillic special + Smalls: Arabic, caps: Hebrew 3 Some Latin/Greek/Cyrillic 4 Bopomofo 5 Hiragana 6 Katakana
from http://vim.runpaint.org/typing/inserting-accented-characters/