If you have time, the Omaha Botanical Gardens is a good side trip, and right off the interstate right after you enter NE on I-80 west. The largest nursery is probably Mulhall's (120th & Maple). It is also close to the interstate. I also like Indian Creek Nursery (N. of Dodge on Saddle Creek), Havers is the place to go for pond plants & fish (80th & Maple), Sunrise Lawn & Garden is one of my favorites (N. of I-80 on 84th St exit at 8529 Frederick St--across from Shopko).

Here is a link that might be useful: My pics from Omaha Botanical Garden (Lauritzen Gardens)