My partner and i have decided we would like to travel for 3 months and see some of the world. We are looking at the possibilty of going next May. Any help/advice/information would be greatly appreciated and niehter of us really know where to start! At the moment we are looking into places that we would like to visit and at the RTW flight tickets....
It's really difficult to answer questions like that in general, but the possibilities are endless of course.
I don't where you from, but assuming you are from Europe, a regular (cheapest) RTW ticket usually can include a stop in the USA, the Pacific (Fiji or Cook Islands for example), New Zealand/Australia and Asia. Prices start from around 1500 GBP or so.
With 3 months I suggest you don't go buying more expensive tickets, but spend you money in places suggested above. It's also a nice time for all of these places, except maybe SE Asia, which has the start of the rainy season and is better visited November to February or March.
But summer has started in the US, it's the dry season in the Pacific, the Northern Island of New Zealand is still fine (not very warm though, South Island better not in June or July), and the dry season is also on the role in the northern part of Australia.
It's a very broad answer as well, but it's a start!
I recently looked into a RTW ticket for an 8 month trip I am planning and the problem with these tickets is that they penalize you for taking land routes. For example, if you fly into Cancun in Mexico and travel to Panama City by land to fly out, they will count the mileage traveled on land against you as if you were flying. The RTW is only good if you always plan to depart from the same place you fly into, which in my opinion takes away from the adventure.
In terms of what to see on a 3 month trip, if I was you I'd concentrate on one area of the world, fly in and just land travel around. It's too short a time to do multiple areas, and I always find travelling on land using local transportation to be a great part of the whole experience. You see more and interact a lot more with the people in the countries you are visiting. To give you an idea a small country like Panama took me and my wife 3 weeks and we didn't even get to see everything we wanted. We only got to see about half of Peru in 4 weeks and had to completely abandon our plan to see the Amazon (we're making up for that this time!!).
My personal 3 favorite areas would have to be Central/South America and South East Asia, but I like to travel to places that are a bit less developed, so think about what it is you'd like to see. Each can be explored in 3 months.
Then again, everyone has a different style, and some people really like the quick land, take a picture, and keep going experience. Do what you feel will give you the best experience, either way I'm sure you won't regret it!
Hope this helps