There are some .net ports of the scintilla component, wich is free and very powerful, otherwise you can use the Quantum whale syntax editor, wich is a very very good script editor control, or you can use the Actipro syntaxEdit control, wich is very popular but sucks. If you're used to the wonderfull divelements components, (so you're not used to resource eater components) I would recomend you to take a look to quant whale syntax editor instead of the ActiPro one.