I suppose it might help if I add which things concern me! As I'm a first time mother and am really not sure if these behaviors are unusual or not.
He often head-bangs when in his high chair and car seat.
Scratches at himself (and leaves marks) when he is tired and/or angry.
Walks on tip-toe sometimes.
Plays quite repetitively at times, building towers of blocks and knocking them down over and over again, and lining up his cars along the edge of the coffee table before sweeping them all to the floor. (Though he does play appropriately too).
Has extremely limited speech - only a few words, which he doesn't really use unless prompted.
Wary of new situations. Takes him a while to adjust and will cling to me or DH until he feels comfortable.
Extremely independent, and will only point to something he wants as a last resort - generally he tries hard to reach it himself first and often pitches a fit if he can't get it. Sometimes he even gives up without attempting to seek help.
People often describe him as an observer, and someone who is taking everything in, assessing the situation and figuring everything out. He is quite a serious looking little guy.
He tends to get very focused on whatever he is doing and often doesn't respond to attempts to get his attention. (Though this could possibly just be a family trait as his dad, uncles and many of his cousins are very single-track people who tend to tune out the world when they are busy.)
Eye-contact is slightly hit and miss. Most days I think it is fine and appropriate, but there are times when it is 'off'.
Goes utterly berserk when you try to change his nappy, screeching and thrashing and trying to escape.