First, Matt wrote about C&C expansions and it really seems like the answer is a resounding NO.
OK, I'm going to do you a big favor here, because I was planning on keeping this little gem to myself:
www.ebay.com/itm/Heroscape-MASSIVE-terrain-lot-approximately-RotV-x5-/140811018175?pt=LH_DefaultDomain_0&hash=item20c8fd9fbf
That's enough terrain to play Heroscape forever. Then after that, pick up whatever you can get cheap, like ROTV fogures (the base set) and SOTM (the second base set) worth of figures.
~I WARN YOU NOW~ Heroscape is worse than crack. You will have the unbelievable desire to BUY THEM ALL. Do not. Not all figures are worth having, to be honest.
If you don't want Heroscape (or already own it) then you may want to consider getting any game in the top tier here:
superflycircus.blogspot.com/2010/03/index-of-articles.html
I would recommend highly these:
Ascending Empires
King of Tokyo
Incursion
There's others, but those are what I'd buy if I had 75$ to burn.