chit-chat
crisscross
dillydally
flim-flam
gewgaw
mishmash
nicknack
pish-posh
riffraff
singsong
tick-tock
tiptop
zigzag
Why always a front vowel and then a back vowel? Always "mishmash", never "mashmish".
(Note that words like "tactic" are not instances of this reduplication pattern.)
