Well, you have a lot of different options, and you're going to have to do a bit of research and find out what option is best for YOU and your family.
What I can do is give you an admission 101, so you can determine what TYPE of admission you need, and then I can tell you different places that sell Disney admission.
Disney has four seperate major theme parks: The Magic Kingdom, Epcot, Disney-MGM Studios, and Animal Kingdom. It also has two water parks: Blizzard Beach, and Typhoon Lagoon. There is also an indoor, interactive theme park called DisneyQuest. They also have a nightlife entertainment district called Pleasure Island. And lastly, they have a Sports complex called the Wide World of Sports.
Each of those requires an admission ticket. What type of ticket you purchase will determine what you can and can't do.
SO, on to the tickets!
1 day/1 park tickets: This type of ticket will get you into any one of the four major theme parks for ONE day. It does NOT allow you to park hop. What that means is - let's suppose you start the day at the Magic Kingdom. If you leave, and go to your hotel, you can ONLY go back to the Magic Kingdom. These types of tickets can ONLY be purchased at the ticket windows at Disney World.
Park Hopper tickets: These types of tickets will allow you to park hop for the number of days the ticket specifies. If you have a 4 day park hopper ticket, you can go to the four major theme parks as many times as you want for 4 days. Unused days NEVER expire.
Park Hopper Plus tickets: These type of tickets work the same way as the Park Hopper tickets. What makes them "plus" is that they come with a number of admissions to either of the Water Parks, Pleasure Island, or the Wide World of Sports. The type of ticket you buy will determine how many of those plus admissions you get. AND - the plus admissions are completely seperate. So let's say you have a 5 day park hopper plus. You could go to the Magic Kingdom and Epcot on Day 1, Animal Kingdom on Day 2, Disney-Studios on Day 3, back to the Magic Kingdom on Day 4, and hit all four parks on day 5. Then, on day six, you could go to a water park. Does that make sense? I know it may seem confusing!

Unused days, as well as unused plus admission NEVER expire.
Ultimate Park hopper tickets: These tickets are ONLY available if you're staying at a resort on property. That means a Disney resort, the Swan, Dolphin, or any of the hotels on Hotel Plaza Boulevard. They will get you unlimited admission into EVERYTHING on property for your entire stay. (notice this includes unlimited DisneyQuest admission whereas the Park Hopper Plus tickets do not)
Annual Passes: There are two types of Annual Passes. There's a Premium Annual Pass which works like an ultimate park hopper ticket for a full year - only you don't need to be a resort guest to get it. Anybody can get it. The other type is just a plain 'ol Annual Pass. It works like a Park Hopper ticket for a full year.
Where can you get the tickets?
The Disney Company: There's lots of ways to get the tickets direct from Disney. If you get them direct from Disney, there's a slight discount for purchasing them before you get to the parks. If there's a
Disney Store near you, you can purchase them there. You can purchase them from Disneyworld.com, and you can call 407-WDISNEY to buy them. Here are the types of park hopper and park hopper plus admissions you can buy direct from Disney:
Park Hopper tickets:
4 day
5 day
Park Hopper Plus tickets:
5 day (comes with 2 plus admissions)
6 day (comes with 3 plus admissions)
7 day (comes with 4 plus admissions)
Ultimate Park Hopper tickets:
These can ONLY be purchased from 407-WDISNEY, and Disneyworld.com. They are tied directly to your resort reservation, and are valid from the day you check in until midnight of the day you check out. If you need to, you MAY be able to drop your arrival or departure day. You'd need to speak with someone at 407-WDISNEY for that option.
The websites below have a constantly rotating inventory. So it's impossible to list what they'll have. Go to the sites and check them out:
Ticketmania.com
DiscountOrlandoVacations.com
Mapleleaftickets.com
AAA - again, inventory varies by location. If you're a AAA member check them out.
Hope that helped somewhat!
