The creatures that were placed on top of the ark of the covenant were Cherubim. They are also on the wall hangings in the tabernacle that was used in the desert, and on the walls of Solomons temple. In a previous post I gave the bible texts where the description could be found.
Also interestingly enough, Satan is a Cherubim. You will see this in the book of Ezekiel Ch:28 vs. 11-20. Many people will say this is a description of the King of Tyre, but if you read it in it's proper context you can see how foolish that assumption is.
It's true that it begins by saying ...take up a lamentation upon the king of Tyrus... But a couple of verses on it says ...you were in Eden, the garden of God; So it isn't refering to the human king of Tyre at Ezekiel's time.
A few verses farther on it says...Thou art the anointed "cherubim" that covereth... Thou wast perfect in thy ways from the day thou wast created, till iniquity was found in you. ...I will destroy thee O covering cherub...

This language is very similar to what is found in Isaiah Ch:14 vs.4-22 It starts out as a proverb against the king of Babylon, but in verse 12-15 it begins to refer to Lucifer and his fall from heaven.

You are correct reylari, in stating that many times when men saw angels they had the appearence of ordinary men. This would be strong evidence to me that angels have the ability to change their form at will. Or they have the ability to make us believe we are seeing something one way when it is actually another. I really don't know which it is. Either way they are creatures who were endowed with more power than we have. Hebrews Ch: 2 vs. 6,7 says ... What is man that thou are mindful of him... Thou madest him a little lower than the angels...