If you have too many Friends in your Facebook account, its will be a big issue to have lots of online status in your Chat room. You will be visible for all of your friends when ever you are in online, even though you don't like to chat with them all. But in Facebook Chat have a very nice feature to hide your online status on your Facebook Chat from certain contacts.
First create some meaning full friends list, and then you can choose which of these list members get to see you online. For some Friends list you can simply click the "Go Offline" in the Chat room. And go offline for them.. If you like to be in online with them back then click "Go Online". So you can stay visible to those friends list while the rest of your Facebook friends won’t know if you are logged into Facebook.

Earlier you had to completely turn off Facebook chat in order to hide your online status from other contacts. But now you can do it for some group.. Enjoy..!