forget tablets just buy yourself a pair of gloves and draw in the sky http://www.essentialreality.com/p5_glove.asp

well anyway if you realllly need one the wacom graphire (a6 size) is a good one to start with. you can get a cheaper version without mouse. i got mine for 45 euro. anyway any more would be a bit overkill maybe a5 but no more... atleast not for animation drawings.