Bitcoins (highly secure but slower) = for high end and mid priced items like houses and cars

Litecoins (less secure but faster) = for lower priced items like computers and GPUs

Peercoins (no ending supply like fiat currencies) = for everyday use like buying coffee and snacks

Namecoins (for domains) = they're outside of ICANN control and thus avoid domain censorship

Primecoins (for science) = searches for prime numbers

Dogecoins (doge style) = for donations and sponsorships

Again, any of those cryptocurrencies can be used for anything.