I recommand the Shin Yeh restaurant at No.34-1, Shuangcheng St., Jhongshan District, Taipei City. Its the original restaurant of the Shin Yeh Group, recently celebrated its 30 year annaversary.
This restaurant is famous for its Taiwanese cuisine, (sweet patato porriage) with local favorites such as si gua (sponge cucumber), dried fish w/ peanut and others.
Website (Chinese only w/ a map):
http://www.shinyeh.com.tw/taiwan_a.htm
Enjoy!^