Which best flash for my Canon 7D?

Hello friends

I have been working some overtime and have an 'extra pay packet' coming my way soon. I will be putting some to very worthwhile causes (eg helping Japan's needs, my church, mission work and other charities). I also hope to buy my first external flash unit.

Since getting my first DSLR (Canon 350D) in 2005, I've not had a flash unit. I have used a few from friends, mainly Canon 430EX and 580EX. I also have a Canon 7D which I've had for some time now. I'm tempted to buy a Canon 580EXII flash unit (price is ok for me) - but if I can get more bang for my buck (eg another brand that has more power, better interface, richer feature set, etc) - I'm open to that.

Generally I seem to be very happy with my Canon lenses & accessories, and like the idea of ensuring full compatibility. (I have a Sigma 10-20mm lens which has a very minor decentring issue, but I can work around that).

The other main lenses I have and those that I think I'll use the flash most with on my Canon 7D are the Canon 15-85mm, Canon 100mm macro and Canon 70-300mm L. I guess the situations that I'll mainly use it are: wildlife, 'events' (eg camps and church functions) and occasionally portrait. I'm not a 'studio' person (generally preferring natural light & outdoors - but I know there's a place for flash and indoor & studio work too). Also I am not looking to go to any professional paid work like weddings, paid portrait.

But I do take my photography seriously (as a hobby). I also have a few other Canon lenses, eg 28-135mm, 50mm f1.8, 18-55mm. I have an inexpensive but practical enough macro flash ring for close up / macro work. It's a $30 Chinese made version which I'm happy enough with.

There are various people on these forums whom I have seen use external flash to improve nature shots (eg highlight colours of birds / wildlife, flowers, etc). I know I still have a lot to learn with flash, but I do understand the basics and principles.

Also, do they all flashes have the same infrared / focus assist capabilities (eg power, ability, functionality)? That would be also a HUGE selling point for me - for example when I'm taking shots in very low light and I want to use the focus beam function to achieve AF (but NOT fire the actual flash).

So I very much look forward to hearing from you with your thoughts and advice (please list pros and cons where you can) of what flash I could get. I am glad the 7D can remotely fire flashes from it's built-in flash. I already have a good Manfrotto tripod (and cheaper one).

My budget is up to about $700 Aus (the US $ is around parity with the Aus $ at the moment). Thanks in advance for your posts and suggestions about external flash units for my 7D and various lenses (and the 'why'!)

Paul