Kellogg's All Bran Buds is absolutely packed with fibre. 12 grams in a 28 gram serving. Thats 48% of the percent of daily value, so 2/3 of a cup and you've got pretty much all the fibre you need.
One of the few cereals to contain Psyllium Fibre (may cause an allergic reaction in some individuals). Comes in a 500g box.