You can go to this website and go down a bit:
What Guinea Pigs Can and Cannot Eat

when giving them fruit, only give it as a treat as your piggies can get mouth sores as fruit like apple are acidic.

Bell peppers are extremely good for them, very high in Vitamin c

Mine have apple on occasion, califlower leaves, spring greens, cabbage, carrot, kurly cale, romain lettuce on occasion, banana be careful can give them constipation, Broccoli, celery, fresh grass, dandilion leaves, cucumber, spinach not to much or to often can cause bladder stones, cherry tomatoes with no green top thats poisonous, parsley, grapes, sweetcorn - corn on the cob and finally pear.

__________________
20 or so Guinea piggies,
2 giant rabbits,
3 pet rabbits,
6 gerbils,
3 budgies,
3 cockatiels,
2 chinchillas,
4 degus,
1 hamster,
oh and 1 cat!