I have the 360D. I also have a Nikon Sb400 (had it first). I would ask what you want to do with it. I like the 360D for the swivel/bounce and the power it has. However the iTTL isn't as predictable as the SB400. As mentioned above, if you just set it to iTTL and go then it will blow out some pictures. You really have to watch your exposure compentation, especially if you are bouncing. The Sb400 doesn't swivel, but it does ceiling bounce. I've never had an exposure with it that was unexpected.
If you want a little bit of extra power, the ability to bounce on the ceiling, and a bit of separation between the line of flash and the lens centerline, then the SB400 is a nice little flash. It is very small, charges quickly, and doesn't drain batteries much. With a little diffuser, you can make great straight on pictures.
If you want to do off camera flash, or swivel+bounce flash, or if you want to use manual flash then you need to go bigger like the 360D. It is much bigger, so I would try one if I were you and make sure that you don't mind a big flash on the camera. I picked mine up used on here for £40, so if you can wait until you hit your classifieds limits you can probably find one then around that price and save yourself some money.
Thanks,
Rick