Advice on which Nikon flash to use?

I'm planning to acquire a flash for Nikon D80. I need it to shoot at events like weddings and so on. Please advise me which flash is better to use in this situations - can I use Nikon SB28 or Nikon SB-400, or do I need to buy Nikon SB-600?

Huge thank you in advance.

The SB600 or the new SB700 has power and adjustability that you will probably find useful. The cheaper flashes could be okay sometimes, but there's a good chance you will find yourself coveting more and wishing you'd bought the fancier unit to begin with.

The SB-28 uses a different sort of flash metering than your D80 (d-ttl instead of i-ttl), so it will only work in full manual or auto mode. Not a bad thing, if you know how to use either of those modes.

If you want point and shoot ease of use, you will need an i-ttl flash. That means SB-400/600/700/800/900. The SB-400 is not a flash for weddings or events, it lacks power for such work. The minimum flash to consider is the SB-600, and it is also way underpowered for such work, but not as bad as the SB-400.

Get as much power as you can afford, because if you don't now, you will later.

You should buy Nikon SB-600 Speedlight Flash for Nikon Digital SLR Cameras

Easy-to-view LCD with 6 simple-to-understand backlit buttons
FV lock holds flash value, enabling recomposition prior to shooting
Accurate i-TTL flash control achieved through flash exposure monitoring control
Ready light located beside the LCD on the back panel - highly visible even when used as a remote
Auto zoom of 24 to 85mm, extendable to 14mm with built-in wide-flash adapter