ScriptAculoUs autocomplete web control from SimoneB is a nice lightweight easy to use ASP.NET autocomplete textbox control with many virtues. The only problem I had with it was that dropdown autocomplete list has no scrolling and so long autocomplete lists look ugly. Happily it comes with sources so I hacked it to add scrolling, here is the solution in case somebody needs it.
StringBuilder returnValue = new StringBuilder("<ul class=\"autocomplete\">");
UL.autocomplete { height: 10em; overflow:auto; }
render: function() { if(this.entryCount > 0) { for (var i = 0; i < this.entryCount; i++) { this.index==i ? Element.addClassName(this.getEntry(i),"selected") : Element.removeClassName(this.getEntry(i),"selected"); if (this.index == i) { var element = this.getEntry(i); element.scrollIntoView(false); } } if(this.hasFocus) { this.show(); this.active = true; } } else { this.active = false; this.hide(); } },