Flop set, Ace hits turn, what next??

[Wes ManTooth]

SNG NL, (9 handed) converter

Hero (t800)
MP1 (t770)

Preflop: Hero is UTG with 9[img]/images/graemlins/club.gif[/img], 9[img]/images/graemlins/spade.gif[/img].
Hero calls t15, <font color="#666666">1 fold</font>, MP1 calls t15, <font color="#666666">3 folds</font>, Button calls t15, SB completes, BB checks.

Flop: (t50) T[img]/images/graemlins/spade.gif[/img], 4[img]/images/graemlins/club.gif[/img], 9[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(5 players)</font>
SB checks, BB checks, Hero checks, <font color="#CC3333">MP1 bets t30</font>, Button folds, SB folds, BB folds, Hero calls t30.

Turn: (t110) A[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>

I am first to act what would you do? discuss

I will have another question shortly, explaining my actions and the river.