Flash for the D40x

Morning all...happy father's day for those that it applies to
anyway...I can't find my konica flash that I used to use with my G5 (it's a super old one that I have no idea where I put).
So now I'm thinking of buying a new flash for the D40x and...well I'm tossing up between the SB-400 and 600 in terms of useability and value.
What features make the 600 (or even 800 for that matter) worth the extra bucks and what would you recommend for a DSLR newbie.
cheers!

anyway...I can't find my konica flash that I used to use with my G5 (it's a super old one that I have no idea where I put).
So now I'm thinking of buying a new flash for the D40x and...well I'm tossing up between the SB-400 and 600 in terms of useability and value.
What features make the 600 (or even 800 for that matter) worth the extra bucks and what would you recommend for a DSLR newbie.
cheers!