One of the things that I like doing is having a summary sheet that has all of the important information about the characters (OB/DB, hits, PP, spell lists, primary skills, etc...). Basically enough information so that I could run (or have somebody else run) a character if the player isn't there for a session.
Then during play, I will occasionally ask for a dice roll. Sometimes I will have a purpose in doing that, other times I won't. In all cases, I will always jot something down on my clipboard (I always keep a clipboard for making notes and for having important data on, with a blank sheet on top to hide any adventure notes underneath). When I don't have a specific purpose, I track the rolls and use them for later rolls that I need done in secret.
I have also used the same mechanism as Justin has - a list of pregenerated rolls for those times when the player shouldn't know actual success or failure.
I also have a tendency to ask a player to roll and add skill bonus xx, and then I will add in all the pertinent modifiers myself and tell him the results. That means that even with relatively good rolls, the player won't be absolutely positive about the actual result since they have no idea of the modifiers involved.