Dozens of them...

The important ones in town are

• WAT PHRA SINGH
• WAT CHEDI LUANG - beautiful large brick stupa, try to go after sunset, beautiful lighting
• WAT SUTHEP on the mountain - view on the city, very touristy, lot of shiny gold - Suthep is the Thai word for 'enlightment'. To get there go to north gate, there is a step up point, for red taxi, 60 THB per person; they wait till they are full. You can walk up in 2.5 hours with the Monk's Trail (second part of the trail is relatively hard/uphilly)
  
  

• WAT PHA LAT - beautiful jungle temple, halfway up the mountain to Wat Suthep. Consider walking up there. Navigate to 'Monk's trail' or 'Cafe basecamp'; in 45/60 minutes you reach Wat Pha Lat
• WAT UMONG - tunnel temple outside of town
• WAT LOK MO LI - close to the north gate, you can water the plant in the pagoda with some cable-system
• WAT MAE KAET NOI - horrible temple showing how thai people think hell will look like. 15km outside of town (45 minutes)