I've felt spirits many times. An old woman I felt tell me to call her "Nani", a cat that kneaded my lap while I was working OT, a small boy that curled up against me on my lap and fell asleep. I can't see them, but I feel them.
I've seen the outline of one against the night sky in AZ a long time ago...he was my protector, and had just caught back up to me after asking my best friend where I went. (Long story, but she had a really neat experience with him.)
Now, I feel the energy brushes from my late husband. He brushes along the back of my neck to let me know he's near, he's kissed me, and held me as well since he died. And yes, I've no doubt it's him. The neck brush was a signal we arranged before he died. (Kinda wishing we'd chosen something else now...it feels like spiders on my neck.) The kiss...well, others that I know that can see have let me know by describing him that it's him, so now I know the feel of his energy brushes as opposed to those of others.
Twice, before he went to hospice, I felt the presences of those who came to guide him home...he was very close to crossing over those two times.
Oh...and I saw a black cat running alongside my dogs on our way outside one night, and when we turned toward the door, it kept going through the wall. (They can, apparently, get outside faster than we can.)
Nice thread...and you've gotten some other really great responses.