It will depend on the style of aperature blade, and the aperature. The smaller the aperature, the more defined stars you'll get. The sharper the aperature blades, the more defined stars you'll get. It has little to do with the shutter speed, (although they'll lengthen a tiny bit with a longer shutter, and generally you'll need a longer shutter to accodomate a night shot with an f/11 - 22 shot).
the 14, for instance, has VERY rounded blades, so you'll have a hard time getting much starlike from it.
The 10-24 is a bit better at it. the 18-55 also.
The good news is that a large number of older, cheap lenses tend to have sharp blades. If you find somehting with an odd number of blades, you'll get double the number of bursts as you do blades. If you have an even number, it's the same. (so, 4 bladed aperatures have 4 lines. 5 have 10 lines, 6 have 6 lines, 7 have 14 lines, etc).
Rokinon/Samyand 12 is decent, voigtlander's 15/3,5 is great, and there are many many others. Bokeh on these won't be as pleasing wider, because of the sharper blades.
