Trailing Lobelia "Crystal Palace" immediately springs to mind.

Laurentia has a soft lilac/blue flower.

Scaevola (possibly Blue Wonder) is very popular here in the Czech Republic as a trailing plant for baskets. It flowers non-stop throughout the summer, with very little attention needed apart from watering and trails beautifully.

I also have it in my raised beds in both blue and white.

I was trying to remmebr that one cestina. I could see it in my minds eye but not the name.

I could only vaguely remember the Czech name but not accurately enough to track it down. Then, as I went and looked at mine, it suddenly popped into my head!

Bacopa blutopia. It is easy from seed and not meant for landscaping. It really fills a basket out.

I don't think Lobelia Crystal Palace is trailing, is it? I always go for Lobelia 'Saphire' dark blue with white eye.

lobelia ricardii ...one plant will take up quite a lot of space, its a much bigger species than the normal lobelia.

Thanks to everyone, your answers were great.