Siberian Squills (Scilla Siberica).
The flowers of this little bulb are a most vivid sapphire blue, and you should certainly have some either on your rockery or in front of your border. They like a sandy loam, so if you have a clay soil you should get some sand and plant your bulbs in it. Set them two inches below the surface any time from July to September. They will increase if left undisturbed, or you may lift the bulbs in June and carefully separate the little offsets.