Cost is a big factor for wildlife - good wildlife lenses get expensive really really quickly (sadly its one area that is expensive in photography unless you are very good at tracking).
For wildlife and zoo you could consider:
70-200mm f4 or f2.8 lenses - a good range for zoo shooting and the variable zoom is very useful as subject size and distance changes a lot in that environment.
In an ideal world a f2.8 IS MII would be the best option - that you can also get teleconverters for and push to a 140-400mm lens for wildlife situations.
300mm f4 IS L - 400mm f5.6 L - 100-400mm IS L = each of them is a good solid wildlife lens and the trio are some of the most hotly debated for those getting into wildlife. Each one delivers good results, but each one has its own specific properties to consider. Also note the 70-200mm MII mentioned above when used with the 2*TC equals around the same optical performance as the 100-400mm mentioned here - making the shorter zoom a good option for combining the two uses if one so desires.
From then there are some much more expensive lenses.
Wideangle wise you might find the reviews over a Juza's site of help (he also lists a lot of good general nature article and reviews on the longer lenses as well)
Juza Nature Photography - Articles
Scroll down for reviews and articles - he's covered most of the super wide angle lenses for crop sensors.
A personal note - the 70-200mm range I find is also a good landscape lens, not for those super wide shots, but for isolation of those select features within the landscape (and yes reading this you can tell what lens I might be a fan of

).