check out - this current cost monitor http://www.currentcost.com/
haven't any experience of it but as it spits out xml data should be manageable to get the data into LMCE, I haven't gotten around to doing any investigation but was thinking along the lines of something like a climate plugin I saw mentioned in the wiki - although I haven't seen it in operation, but am assuming it would display local weather conditions. In this case it would be power related data. There is another blog on it here http://dalelane.co.uk/blog/?p=389
Someone else correct me if I am wrong but I think the seluxit viaSENS controller does the power monitoring - but only when the z-wave devices support reporting back the power info to it. The seluxit.com website seems lacking in info - thought there used to be more there??