Hello Molly! There are so many great resorts at Disney! It sounds like a water slide at the pool might be important to you. If so, you should know that although the value resorts are most affordable, they do not have water slides in their pools. So you might want to look at a moderate or a deluxe resort. For the moderate level, I enjoy Port Orleans. It's a peaceful resort with a nice pool with a water slide and you can also take a relaxing boat ride to Downtown Disney.
If you are able to afford deluxe, you may want to check out the Beach Club - the pool area is literally a mini water park. Another option is the Polynesian which has a neat volcano pool (where the slide is on the inside of the volcano). You also have the added convenience of the monorail at the Poly.
In case you didn't know, Disney is offering a great package on most nights through 3/27/10 which may make your vacation more affordable. If you book a moderate resort (or higher level) for 4 nights, you will get an additional 3 nights at no extra charge. You can read more about this great package
here.
I hope this helps - please let us know if you have any follow up questions! Diane