Best trilogy.

[Regeza]

For me it is MAB vs Terrible.

[The Big Dunn]

ali v frazier.

[Rico1965]

Gatti vs Ward

[TGD]

Gatti - Ward

[pugilistprophet1994]

Hmm, Barrera-Morales.

[Tay Roc]

Marquez v. Vasquez I-III.

[Polaxed]

Holyfield vs Bowe.........closely followed by Barrera vs Morales.

[sinmiedo]

izzy vazquez vs rafa marquez (although i know there were 4 but that one wasn't the same with izzy eye not being healthy and all)
gatti vs ward
mab vs morales

[Regeza]

Man, so many great ones. Bowe vs Evander is my second.

[FeFist]

Ali v Frazier.
Marquez v Vazquez 1-3.

To be honest most trilogies are memorable, you wouldn't exactly stick two fighters with zero chemistry in the ring 3 times.