I suppose that would depend on how much you want to spend.
I think these guys make the best safes out there:
http://www.hallsafe.com/
Fort Knox is probably equal in value.
http://www.ftknox.com/
I would hope you plan on getting more guns in the future and that you plan accordingly. Get the best one you can afford and plan for that future. You know what you are protecting. Firerating is a must.
http://www.libertysafe.com/Safe_Centurion23.lasso
Liberty safe makes a nice entry level safe that cost me about $700. Fire rated to 1200 degress for 30 minutes. It holds 20+ long guns.
I bought it a couple of years ago at a hardware store so I could store some toys in my basement of the home I now live in.
OR, you could put them in one of my safes....