kbenoit,
You may want to ask some of the wheel building specific questions over in the Mechanics forum. There are a number of threads there with excellent wheel building help if you search.
There are different thoughts on reusing spokes. And yes, unless the rim you change to has the exact same dimensions you would need new spokes (assuming you reuse the same hubs -- Are you going to reuse the hubs?)
As to a replacement rim -- there are many options in 28 or 32 hole. Mavic Open pro are a standard. Other options are DT Swiss R1.1 or R1.2. Velocity also offers some less expensive and solid rims like the Aerohead and Deep V. Then there are all the new carbon fiber rims as well (much more expensive).
Tell us what kind of riding you do and that may guide some feedback.