IMO:
Five Icon Dock
Five Column Springboard (Haven't been able to find this yet though for iOS 6.1 JB)
SBSettings or NCSettings (I prefer SBSettings - slightly more features)
KillBackground (Again, not sure if this is 6.1 JB compatible yet, but VERY useful for quickly closing all apps and freeing up RAM)
Those are my favorite must-haves for past Jailbreaks.