If you are curious to know the average CPM rates for online advertising across verticals, this graph from Adify should give you a good idea.
CPM trends across verticals
Except Food, Entertainment and Real Estate, the CPM rates for display ads have declined across industries in the last three quarters which is quite good news for online advertisers but not so good news for web publishers and bloggers.
For some unknown reason, this Adify Report excludes the Technology sector which also commands high CPM rates (the CPM rates for tech industry were around $15 in Q2 2009).
CPM = cost per thousand ad impressions.