Trezor is a reliable hardware wallet for storing bitcoins.
I have also tested the popular Ledger wallet, but I find the Trezor device easier to use.
Trezor is Windows, OS X and Linux compatible.
You can backup your bitcoins by copying down a secret passphrase (on paper). You can use this passphrase to regain access to all your bitcoins in case of disaster, loss or theft.
Trezor code is open-source and technical decisions are discussed with the wider developer community. Everything can be audited by an independent third party.