This title is slightly misleading, I should replace it to Beauty Shopping at Ximending, Taipei because this was where I camped spent all my free time.

Taiwan is full of personal care stores and I am only going to address the leading ones. Judging from the perpetual flow of customers, these stores seem to have a leg up on the competition.
And please accept my apologies for not taking pictures of the stores or the displays because I was being an extremely good shopper/bad blogger.
① 86 Shop
Address: 台北市萬華區成都路27巷5號1樓
Telephone: (02)2370 6257
Hours: 周一至周四 13:00-21:00; 周五至周日 13:00-22:00
Brands: 3CE, Bevy C, Bioderma, Bonanza, Cremorlab, Dr. Hsieh, EJG, Hanaka, Miss Hana, Solone

② Cosmed
Address: 台北市萬華區成都路54號
Telephone: (02)7729 8278
Hours: 09:00-02:00
Brands: Dr. Morita, For Beloved One, My Beauty Diary, Neogence, Nuxe, Opal, Shiseido Senka, White Formula

③ Mirada
Address: 108台北市中華路一段88號
Telephone: (02)2314 6311
Hours: 週一至週四 10:30- 22:30; 週五.六及例假日前一天 10:30-23:00
Brands: Bonanza, Dr. Morita, Kuan Yuan Lian, Meishoku, My Beauty Diary, My Scheming Beauty, Sexylook, Solone

④ SaSa
Address: 台北市萬華區峨嵋街45號1樓
Telephone: (02)2370 0226
Hours: 11:00-22:00
Brands: Bonanza, Meishoku, Neogence, Nuxe, White Formula

⑤ Watsons
Branch: 武昌
Address: 台北市萬華區武昌街二段37, 39號
Telephone: (02)2388 9107/2388 9108, (02)2389 2346
Hours: 24H
or
Branch: 西門
Address: 台北市萬華區成都路15號
Telephone: (02)2314 0833/2314 7837, (02)2314 7837
Hours: 24H
Brands: 1028 時尚彩妝, Beautymate, Bourjois, Canmake, Cezanne, Dr. Wu, For Beloved One, Kanebo Media, Kose Junkisei Prime, Naruko, Neogence, Unitec

Additional information:
① Majolica Majorca, Integrate, Sofina Jenne, Sofina Primavista, Lavshuca and Kate are found at most places.
② Etude House, Skinfood, Nature Republic, The Face Shop, Tony Moly and Too Cool For School have stores at Ximending.
③ Foreign currencies are exchanged upon arrival at Taiwan Taoyuan International Airport or at banks. Bring along your passport and keep your exchange receipt; it must be presented in order to exchange unused NT$ before departure.
Feel free to leave any queries in the comment section, I will try my best to help!

Taiwan is full of personal care stores and I am only going to address the leading ones. Judging from the perpetual flow of customers, these stores seem to have a leg up on the competition.
And please accept my apologies for not taking pictures of the stores or the displays because I was being an extremely good shopper/bad blogger.
① 86 Shop
Address: 台北市萬華區成都路27巷5號1樓
Telephone: (02)2370 6257
Hours: 周一至周四 13:00-21:00; 周五至周日 13:00-22:00
Brands: 3CE, Bevy C, Bioderma, Bonanza, Cremorlab, Dr. Hsieh, EJG, Hanaka, Miss Hana, Solone

② Cosmed
Address: 台北市萬華區成都路54號
Telephone: (02)7729 8278
Hours: 09:00-02:00
Brands: Dr. Morita, For Beloved One, My Beauty Diary, Neogence, Nuxe, Opal, Shiseido Senka, White Formula

③ Mirada
Address: 108台北市中華路一段88號
Telephone: (02)2314 6311
Hours: 週一至週四 10:30- 22:30; 週五.六及例假日前一天 10:30-23:00
Brands: Bonanza, Dr. Morita, Kuan Yuan Lian, Meishoku, My Beauty Diary, My Scheming Beauty, Sexylook, Solone

④ SaSa
Address: 台北市萬華區峨嵋街45號1樓
Telephone: (02)2370 0226
Hours: 11:00-22:00
Brands: Bonanza, Meishoku, Neogence, Nuxe, White Formula

⑤ Watsons
Branch: 武昌
Address: 台北市萬華區武昌街二段37, 39號
Telephone: (02)2388 9107/2388 9108, (02)2389 2346
Hours: 24H
or
Branch: 西門
Address: 台北市萬華區成都路15號
Telephone: (02)2314 0833/2314 7837, (02)2314 7837
Hours: 24H
Brands: 1028 時尚彩妝, Beautymate, Bourjois, Canmake, Cezanne, Dr. Wu, For Beloved One, Kanebo Media, Kose Junkisei Prime, Naruko, Neogence, Unitec

Additional information:
① Majolica Majorca, Integrate, Sofina Jenne, Sofina Primavista, Lavshuca and Kate are found at most places.
② Etude House, Skinfood, Nature Republic, The Face Shop, Tony Moly and Too Cool For School have stores at Ximending.
③ Foreign currencies are exchanged upon arrival at Taiwan Taoyuan International Airport or at banks. Bring along your passport and keep your exchange receipt; it must be presented in order to exchange unused NT$ before departure.
Feel free to leave any queries in the comment section, I will try my best to help!