Based on the replies, a Nikon SB-600 is the safest recommendation. It should work well in automatic modes on the D60, F5, and a future D7000, and several users specifically recommended it as a good-value option.

If you want more features, the SB-900 was also suggested, but the SB-600 seems to be the better fit if cost matters.

The general advice in the answers is that most newer Nikon hot-shoe flashes are backward compatible enough to work across these bodies, so buying a recent Nikon-compatible flash is a sensible way to stay flexible for future upgrades.

If you were comparing against Metz 36 or 48, the community consensus leaned toward the SB-600 instead, mainly because it’s proven on Nikon bodies and should cover your current and near-future needs well.

If you later want off-camera wireless control, one answer also mentioned adding an SU-800 controller.