Cedar, teak, iroko and oak can all be used outside and either left bare to take on a nayural silver grey colouring or treated with a clear or coloured stain/preservative.
I'd add that teak and iroko contain natural oils which mean that they can be left entirely without preservative. Iroko is frequently specified for dock pilings and lock gates for this reason (it's also cheaper than teak). Oak will weather to a silver grey if left untreated, but will still last many years in outdoor use if untreated (e.g. church lyche gates, etc)
Think with any hardwood you want to check where it has come from (FSC certificate) and you get a certain amount of what you pay for.
Eucalyptus is quite durable but not as durable as teak. Google the words to get plenty of info.
To my knowledge Teak is one of the best and most naturally durable woods for outdoor furniture and if cared for will survive a lifetime of use. Just oil it to keep looking nice (doesn't affect the hardiness just keeps it looking pretty!!) and slowing the natural weathering silvery colour process.
Bought our teak furniture via wholesaler on ebay a while ago and looks as good as new -applied 3 coats of teak oil when new and then once or twice a year (takes an hour or so for a large set thats all)
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local