With Magic Lantern installed on the Canon 550D/T2i you can get good audio without having to buy separate audio recorders and sync that audio later in post. Many have said that the audio is not good enough for professional use. Period. But if you listen to Mordy here, the audio is perfectly usable for interviews. He also gives some good tips on setting the levels.
Canon T2i/550D with Magic Lantern: DSLR Audio that you can use! from Mordy G on Vimeo.