I absolutely recommend the sites given by other posters. Planning a Disney trip can be very simple or very complicated depending upon how much you want to put into it.
Here are some things I've learned that I can share:
Avoid summer (miserably hot and crowded) and holidays (crowded and you'll pay extra for lodging/transportation) if you can help it. Low seasons in Orlando are the same as low seasons in most resorts -- spring and fall, when the kiddies are in school. If your kids are young, and/or if you're okay with taking them out of school, then by all means target the spring or fall. April and May should be beautiful in Orlando.
You'll also find the best airfare deals in the spring and fall, though Orlando is so heavily traveled that I've never had an issue finding reasonable fares. Personally, I book my airfare first and then look for lodging.
The biggest two decision which will affect your budget in regards to lodging, IMO, are:
1) Is it worth the extra money to stay on site?
2) Do you want a hotel or a villa?
These are very personal decisions. I stayed in a 1 bdrm villa at Old Key West (a Disney property) and didn't regret at all the decision to get a villa. We each had separate sleeping areas and two t.v's, a kitchen and a washer/dryer. With young kids, being in a hotel room would have felt very confining.
However, were I to do it again, I wouldn't be so adamant about staying at a Disney branded place. That's because we never used the internal transportation system nor did we take advantage of the Start Early/Stay Late perks. So it was kind of a waste of money to stay on property. If I were to do it again, I'd definitely rent one of the thousands of nearby TSs and put the money into activities. Note that you can book a week at one of the very nice Orlando resorts (e.g. Marriott or Starwoods) for under $600 for a week most weeks via II Getaways!! That's an incredible deal!
If you simply must stay on site, consider buying Disney points and using them to book Disney branded TS villas.
Other things: Rental cars in Orlando are cheap. Booking a shuttle two ways is sometimes just as expensive as renting a car. See Mousesavers.com for coupons.
There are very few discounts to the parks. Unless you're willing to attend a TS presentation (I'm not) then prepare to pay full price. But, don't overestimate how many days you'll need. We stayed one full week and only spent 4 days at the park.
Don't overindulge the Mouse. My kids' favorite activity, hands down, was the day we spent at Adventure Cove. They swam with the dolphins and still talk about it. It's expensive ($250/pp) but it's an all day activity and it includes admission to Sea World Orlando which helps alleviate the hurt.
Finally, book activities like Character Breakfasts early. Our second favorite activity was an evening cruise to watch the fireworks. You take a beautiful cruise on the lake, park in time to watch the fireworks, then head back to the dock and avoid all the crowds. You can take snacks and drinks on board. Not sure if they still do this, but it was a very nice respite from all the Mouse madness and I highly recommend it.
We always find the park hopper pass to be nice. This way you can go to more than one park a day, without eating up all your passes. Regarding character brkfsts, yes, book early. In fact, book all your reservations early. Disney has a 6 month res window for anything that isn't counter service. I think this is ridiculous, esp since they do not require a cc# for most of these places, which means ppl book their reservations, and if they change their mind, never call to cxl. Most places will take walk-ins, but be prepared for long waits. Meal packages are very helpful too. If you are staying at a resort property, you can charge everything back to your room as well, which is wonderful, just one bill for the entire week. We loved the dining packages. The only complaint we had was that you cannot purchase one for a kid under two, however, you can USE your meals to feed the kid under two (most employees at the park will not tell you this, perhaps they do not know). We did not find out till halfway thru our week that you can use your meal/dining as much as you want. It doesn't have to be limited to a certain number of meals per day. We actually ended up with left over dining credits in our acct when we left disney. You pay for them, but you cannot get money back when your stay is done, so be sure to use up all your meals, snacks, even if it means buying snacks you don't need and taking them back to your hotel room (or taking them home with you). Once we found this out, we started using our dining credits to feed our 2 year old too, instead of paying for his meals.
We also stayed at Olde Key West. I loved the space we had and the option of having a washer and dryer, but the place was a dirty pit. The furniture was old, stained, and torn. The floor was filthy, there were holes in the walls, dead bugs on the window sill in the shower, the shower was very, very dirty, the coffee pot still had coffee in it from the previous person, I could go on and on. Try calling someone, and you get put on hold FOREVER! We found this to be the case in almost every instance we needed to call around for anything. Personally, next time we will either stay off disney property, or find a cheap place at disney (figuring the less you pay, the lower your expectations would be). Disney parks are beautiful, but I was not impressed with how the vacation side of things were run.
Regarding time of year, I agree with previous posters. Any time you can go during off season, you will enjoy your trip much better. April and May is starting to get pretty hot, but nothing like June-Oct. Our favorite part about living in Tampa was being able to run to disney on an odd day and not fighting crowds. Don't get me wrong, Disney is ALWAYS busy. But there is busy, and then there is sweltering hot, elbow to elbow over crowded. that is what you will get June - Aug. I will never go to Disney June-Aug again! My favorite time to go to Disney was Nov-Feb, mid week.
We loved the Polynesian Resort and (renting points at) the Villas at Wilderness Lodge.
