Hilightmemo(by me) - an analogue of a multi-line editor with syntax highlighting, auto-completion, undo and undo rollbacks. Compact, there are over a dozen different compilation options to configure the desired set of features;

VMHSyntaxEdit (by D. Zharov aka Gandalf) - another editor with syntax highlighting, ported from the VCL component;

VMHPasHighlighter - based on VMHSyntaxEdit, specially designed for syntax highlighting of Pascal source text.