I use terrain from warmill gaming accessories: http://www.warmill.co.uk/Street_Wars/cat814919_982810.aspx
There stuff is the perfect scale and look for mega city 1 I also happen to know that in the next few mohts they are going to be releasing some more new buildings that work really well as hab-blocks.
I've also used black cat bases for some of there scatter terrain and small bits and bobs to add character: http://blackcatbases.com/index.php?main_page=index&cPath=430_435
Finally Atenocitis workshop do some fantastic bits: http://www.antenocitisworkshop.com/antenocitis/governance-of-technology-got-scenery-1.html
Warmill is always my go to for the base terrain as there stuff goes together really well and creates a really cohesive look, then throw in a few charcter pieces from other companies and you will have a really attractive, attention grabbing board!
Noc