Depends on what you're using it for. 2.5 will allow you to run 35's and tackle quite a bit. If you want to do it 'right' the first time and maintain factory ride, plan on spending a decent amount of cash. Spring w/ Shock lifts of the likes of Teraflex, Rock Krawler, Old Man EMU, AEV and a few others will come with the necessary parts to make things right and still ride good. The above lifts are pretty well documented here and you can let yourself decide what is right for you. Personally I went with Teraflex because I got an awesome deal on it but was about to pull the trigger on a Rock Krawler lift.
Anyway search around here, there are a ton of folks just like you that are asking for advice on lift kits. Go with what you want to buy but most 'quality' lift kits with Shocks in the 2.5"-3" range for running 35's are in the neighborhood of 700-900 dollars. You could re-use your shocks and get extenders but I don't personally like that idea.
Once you decide which lift, then it's time to pick out some tires! Don't forget spacers or new wheels if you want to keep you stock rims.
....let your addiction begin
Hope this helps. Check out my signature for my build and pics.