River bet with a set

[NNH]

200NL 6max

Reads: Villain is pretty tight overall. Haven't seen him get out of line yet. I just joined a couple of orbits ago, and have raised 1-2 times per orbit.

PokerStars No-Limit Hold'em, $2 BB (6 handed) internettexasholdem.com

UTG ($168.05)
Hero ($204.25)
CO ($172.85)
Button ($69.50)
SB ($68)
BB ($273.65)

Preflop: Hero is MP with 7[img]/images/graemlins/diamond.gif[/img]7[img]/images/graemlins/heart.gif[/img]
UTG calls $2, Hero raises to $7</font>,4 folds</font>, UTG calls $5.

Flop: ($17) 2[img]/images/graemlins/spade.gif[/img] 3[img]/images/graemlins/spade.gif[/img] 7[img]/images/graemlins/club.gif[/img] (2 players)</font>
UTG checks, Hero bets $8</font>, UTG calls $8.

Turn: ($33) 5[img]/images/graemlins/heart.gif[/img](2 players)</font>
UTG checks, Hero bets $21</font>, UTG calls $21.

River: ($75) k[img]/images/graemlins/spade.gif[/img](2 players)</font>
UTG checks, Hero ?

What's my best play here? Also comments on all streets appreciated.