Good flash for starters

[Paul SWD]

Hi,
My main camera use is underwater, and on land outdoors now and then, but recently I've ben asked to do photos for a friend's wedding. I use a Nikon D90 and wondered what flashgun would be ample for the job?
I was wondering if Jessops' own or Currys' Metz £80 "36" flash would suffice?
My other option is possibly £150 on a 2nd hand Nikon SB600 or £240 for a new SB700, which I dont really wish to fork out for at the moment. But owndered what extra capabilities I would get if I got something like this?
I'm thinking all I am after is something that can spread wide enough when using a wide angle lens for group shots indooors or basically one that is high enough to emit light over my long lens.

Many thanks

Paul
www.scubysnaps.com

[Michael Sewell]

Comparison can be seen here (http://www.youtube.com/watch?v=AshEjPuBAaI)
Additional diffuser dome causes the speedlight head to move to its widest possible setting, and the is also a flip down wideangle adapter too.

[Paul SWD]

Thanks for the link Michael but I was looking more for a comparison at the other end, an SB600 or 700 with the budget <£100 flashguns

[Michael Sewell]

General comparison information (http://dpanswers.com/content/nikon_flash_models.php)