There are dozens of different eucalyptus but none are hardy below about 15-20F. J.L Hudson offers 28 different varieties and if I have some extra space some year I’ll order seeds for a few different ones and see how they do. I'm especially intrigued by ones described as lemon scented or peppermint scented. Anything I try has to be fast growing because none can over winter here unless I tried one of the dwarf shrubby ones in a pot. J.L. Hudson sells almost everything for $2 a packet so it's cheap thrills if you like growing stuff from seed.
The two that most people grow as annuals are Silver Dollar and Silver Drop. Silver Dollar (pictured above) has larger leaves, perhaps half dollar sized here in Michigan, while Silver Drop’s are the size of dimes or nickels. Both are nice although I usually grow Silver Dollar because it seems to grow a little faster. In a single season each plant grows into a little shrub about 3 feet tall with lots of useable side branches. They could be fun to grow in an annual bed just for the unique silvery blue foliage and the scent.
They are simple to grow from seed, the Silver Dollar I planted this year on March 8th were all up in about a week.