Not sure what zone you are in, but for dark blue violet you can't beat May Night sage/salvia. Bellflowers are notoriously invasive. I have been digging out creeping bellflowers on my corner for about 10 years and they still keep coming. The only tall bellflower I would recommend is Sarastro, and that isn't spiky...it has big purple bells. Some of the Veronica spicata cultivars might work also. If you want REALLY tall, like 4-6 feet, go for delphinium.
There might be more, but that's what I can think of for now.
