Lots of good info above, I'm going to add a little more.
Photograph all of your guns. Minimum 3 photos for each firearm. One overall picture, One close up of the serial number and one close up of the make and model. Don't forget optics, accessories or engravings. Take your time and get useful, clear pictures. In today's world of digital photography there is NO excuse for a bad photo. If the image is bad, you know instantly that it is bad, and you can do it again. You should be able to read the make, model and serial number from the photo. Once the photographic record is complete, store the digital images on some stable media (CD, USB drive, SD card etc.) Place that media in a safe location OFF SITE, so it will not be lost along with the valuable property. If there is a fire, flood, theft, whatever; you don't want the record to be lost with the items. Place the CD/USB drive whatever at a remote location such as a safe deposit box at a bank, an attorney's office, at your place of business, at a trusted friend or family member's home, etc.
SAFES: As pointed out above, Safes only buy time. They are not absolute guarantees of security when it comes to fire & theft. However, buying time is the best we can do. So, decide how much time you wish to buy and purchase accordingly.
I can tell you from personal experience, I have lawfully breached a full-size gun safe with hand tools in less than 10 minutes. Not some sheet metal cabinet but a $1000, 500 lb. plate steel safe. It's not that hard.
If the thief can get the safe down on the floor on its back or carry the entire safe away - it is pretty much over.
Bolt the safe securely to the floor OR build walls around the safe so it cannot easily be removed or tipped over.
Remember, A 5 foot tall safe provides a LOT of leverage to those floor anchors, so don't cut corners on the anchors. Better still, build walls around the safe so it cannot be tipped.
A vault is the best option (you can't carry a vault away) but not everyone has that option. A safe is the next best option.
A thief cannot attack what he cannot find. HIDE THE SAFE !
The room, alcove, closet, etc. that contains the safe should have an opening smaller than the safe so that the safe will not fit through the door/opening.
Do not rely on the weight of the safe to prevent its removal. If people could bring it in the structure, you can bet your last dollar people can take it OUT of the structure.
Never place a safe directly on a concrete floor. Place the safe on a small pedestal. 3"-5" is all you need. This will prevent condensation both under and inside the safe. Plus, a short pedestal will save you in the event of a minor flood. (Think broken pipe or backed up drain) A 3" pedestal can be the difference between ruined contents and no problem at all.