First you should know that although occasionally jump n hot stuff for short term gains, I primarily have a months to years focus, though I do sometimes trade around a core holding.
I'm playing REE through UCU.V, which also has high grade uranium on its very favorable property in Alaska, as well as CCE.V, which has a Ta/Nb/REE property under development at BLue River in BC, plus Eldor, a Ta/Nb/U/phosphate/Au/REE prospect in Quebec.
For cobalt with a manganese/scandium kicker, I am playing GMC.TO B warrants, which don;t expire till 2012. The key here is financing, but it looks like there will be a cobalt shortage developing over the next year which I hope will loosen the purse strings.
For lithium, I have thrown in my lot with the big boys qho are backing CLQ, to me the best of the brine deposits. (Stick with the brine plays is my advice.)
For its manganese deposit in the US, I loaded up with RD.V at lower prices, but it is still cheap IMO.
My other rare metal plays right now are GXM.V, which needs financing for its Mo/W properties in New Brunswick, and LGO.V, which has a big Mo/W property in Quebec and a very prospective V/PGM property in Brazil and appears to be entering another promotional cycle. LGO management are superb promoters - check the chart over the years
For U I am going with near term producer STM plus MGA warrants, and explorers PXP and HAT.
I also have some copper and a number of gold lpays, but I will save those for later.