I'm preparing for a mini tour in the greek islands this August and I'm getting concerned about sun protection. I'm considering not using a helmet (as I'll reach 30 km/h max). Last year I was wearing a "buff" that protected me from sweat, but did not protect me from minor sunburn. Would a hat be a solution, but of what type (considering strong winds)?
Definitely do something to protect the back of the neck, and your ears (even with a helmet). The other area that it seems often "surprises" you is the backs of your lower legs (though this may be peculiar to the higher latitudes I frequent).
You of course need a sleeved jersey or sun lotion on your arms, and either knee-length pants or sun lotion on the tops of your thighs.
[I'll add that I've several times been on tours with a guy who has "sun allergy", and he does remarkably well in a full-length Tyvek suit. On hot days when you'd expect him to suffocate, he churns merrily along.]
I recommend wearing a helmet and something like a cycling cap or something similar to an Under Armour skull cap that can absorb sweat and protect your head from the sun.
As for your neck, I've always used sunscreen during sunny rides. Get a bottle that can fit in your saddlebag or backpack, and apply it liberally and as often as necessary. Sunscreen will protect you from the sun without impeding your ability to move, and it will not be affected by strong winds.
Make sure it has UVA and UVB protection, check the SPF and the UVA star rating (higher numbers means more protection). Make sure you apply enough sunscreen and reapply it often enough.
There's some fairly detailed information on sunscreen here that you might find useful.
Anything wrong with the traditional cycling cap?
Solar light cap Oasis or Kayak models do well for sun coverage, while additionally providing evening light power (for the touring).