When it comes to U-2s in 1/48 scale, Testor (originally Hawk) makes the smaller early model, and Italeri (connected with Testor) makes the stretched U-2R (TR-1). You can get resin accessories to make this kit even better from Meteor Productions (www.meteorprod.com), and decals, too.
In 1/72, early versions have been produced by Airfix (also packaged back in the 1980s by MPC) and Academy. The stretched "Dragonlady" versions have been made by Special Hobby (Czech) and High Planes (Australia).