If you have homeowner's or renter's insurance, talk to your insurance agent before you purchase third-party insurance plans. You can often get a rider on your home/rental policy to cover specific devices at a significantly lower cost than the cost from independent companies for that one device only. Not always, but it will be worth checking before you buy other insurance.
If you do need to go with a separate company, check out
Safeware. Though I've never used them myself, that's the company my previous university recommended.
Regards.