Air Asia flies from Kuala Lumpur to Banda Aceh.
Four or more times a week.
Firefly , a daughter airline of Malaysian flies four times a week
Unfortunately, you can not get a visa on arrival in Banda Aceh. Therefore, you need to get a visa from the Indonesian consulate in Penang or the Embassy in Kuala Lumpur. The procedure takes 1 to 2 days. If you do not want to loose time at the embassy you can also fly from Penang or Kuala Lumpur to Medan (with Air Asia or Malaysian Airlines ). In Medan you can buy a visa on arrival (25 US$) and fly to Banda Aceh with Garuda Indonesia, Lion Air or Sriwijaya (all are not bookable online).
If you do not want to fly, you can go by boat from Penang to Medan and from there by bus to Banda Aceh.
Sumatra Ecotourism provides valuable information for travellers to Aceh
From Jakarta there are daily flights to Banda Aceh by Garuda and Lion Air.