The Sri Venkateswara Temple at Tirumala dominates everything else — for nearly every visitor, it is the entire reason to come. Plan around the temple first, and fit anything else around the time the queues leave you. There are, however, several other temples and natural sights worth seeing in and around the town.
In Tirumala itself, the Swami Pushkarini sacred tank, the Sri Venkateswara Museum, and the surrounding sacred waterfalls of Akasaganga and Papavinasanam can be visited on the same hilltop trip. Down in Tirupati town, the Govindaraja Temple is the second-most-important Vaishnavite temple in the area, and Kapila Theertham at the foot of the hills is a striking Shaivite temple with a waterfall and pool. The nearby town of Tiruchanur has the Padmavathi Temple, dedicated to Venkateswara's consort, which most pilgrims visit either before or after Tirumala.
For day trips out of the town, the Chandragiri Fort (the last seat of the Vijayanagar Empire), Sri Kalahasti (a major Shaivite temple town), and the waterfalls and trekking in Sri Venkateswara National Park make sense if you have time after the temple obligations.