Corners - well you do need number flashcards for this one. Attach them around the room, children move to one as you count down from 5 to 0, then call out a number and anyone there is out. When children are more confident, those at tables can put heads down and call out number when teacher taps them on shoulder.
Mouthing - silently mouth a number several times facing different directions so that everyone can see shape of your mouth as you 'speak'. Helps children to focus in general and on corect shape of mouth in particular.
Back-writing - the name explains it- write a big number shape on child's back - can they guess it?
Sky-writing- write numbers in the air then children guess.
Forwards/backwards - one person thinks of number, others have to work it out by listening to whether guessed number was too high or low until hopefully they focus in on correct one.
Stamp-it-out - (only works for numbers up to 20?) this is really simple but the kids really enjoy being allowed to stamp in the classroom. Children stand behind desks or walk around room. Teacher calls out a number and children have to stop, stamp the correct number of times as they count out loud. We usually finish with a flourish by making a horizontal cutting action with our arms and calling out "Ça y est!"
Hope you can make use of these simple games :-)