Um, if its "index" and "indices", why not "suffices"?
Funny you should mention that, Tone (no - I was sure someone would raise the matter!), but I almost wrote suffices. Then I decided to check - and guess what? Although the ~ices plural form is given for index, not one of my seven varieties (1960-2005) of Oxford dictionary mentions an ~ices plural for suffix. If it existed, it might be confused with the third-person singular form of the verb to suffice, so perhaps that's why not.
"Style is knowing who you are, what you want to say, and not giving a damn." — Gore Vidal