It is possible to get a fast sea ferry from Penang to Medan on Sumatra in Indonesia which is a great place to start travelling through Indonesia from west to east. There is (or was) a ferry every day except Friday and Sunday and most travellers cafes or travel agents will be able to give you tickets. To save the commission you can just go straight to the ferry companies " Kuala Perlis Lnagkawi are one and Ekspres Bahagia are another (sorry I don't have the addresses or phone numbers). The trip takes between 4 and 5 hours and leaves Georgetowns Swettenham Pier and arrives at Belawan which is the port of Medan and 26 kms form the city. A complementary bus takes you the 45 minutes into town.