what is this knot on the top of my foot,it doesnt hurt but is very noticable

Not sure if this is what you have, but I have a ganglion (sp?) cyst on my right foot. It is a soft ball (about the size of a pea) right on the top of my foot on the big tendon that runs from your ankle to your big toe. I just developed this recently after having bunion surgery on my left foot. My podiatrist told me it was a ganglion cyst probably caused by all of the extra weight and work my right foot was doing because I was limping for so long and not walking normally on my left foot. He said they usually go away on their own, and if it ever became painful, they could drain it.

either what Mambito said or I have a bone spur on the top of my foot (both actually, but the one on my left foot is much bigger).