At 5 months old, they are beginning to have a sense of self, so toys with (infant safe unbreakable) mirrors are a good choice.
Toys with textures which make different sounds are recommended as well. Have you heard of Lamaze/Sassy toys?
Their toys are meant for infants and brightly coloured with different textures and sounds to entertain your baby.
http://www.fisher-price.com/en_US/playtime-guide/5-months/index.html
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