DotnetIL Editor (DILE) allows disassembling and debugging .NET 1.0/1.1/2.0/3.0/3.5 applications without source code or .pdb files. It can debug even itself or the assemblies of the .NET Framework on IL level.
DotNetIL generation library built on top of System.Reflection.Emit. Allows nice looking C# IL generation, typechecked opcode parameters and IL block manipulation.