There are many mind-mapping tools out there and I tested at least 5 (Mindmeister, XMind, Mindmanager, GitMind, Ayoa, etc), but Mindomo won me over with two key features: file attachments
(you can even search for images online directly from Mindomo, besides normal upload) and real-time syncing between my PC and phone (that actually worsk). It's amazing to start a project on my laptop and continue on my phone without missing a beat!