This probably doesn't count as a sourcebook, but I voted for "other" ... I would like to see more of the map packs.
The quality of the Catalyst maps is absolutely amazing! and I LOVE the tiles that came in the Lakes & Rivers and Cities & Roads sets! I have both infact. And even got the bonus dropship tile for preordering the Cities & Roads set!
I ALSO have Map Compilations 1 & 2 which were all FASA reprints, as well as the all original Map Pack 7 from FanPro (which is actually designed for all 9 maps to be able to be used together!).
I'd like to see MORE sets with high quality maps and MORE tiles because of how versatile they are.
* A wider variety of tiles would be cool though - canyons/chasms, other dropships, larger buildings, gun emplacements, defensive walls, etc. all of these would be VERY cool!
* A new assortment of map designs would be great too! Map Pack 7 from FanPro gave Us a military base/space port (SO COOL!), but how about a mech repair facility or something as large as an entire city, a mountain range/ridgeline? how about BRAND new combat arenas with new and interesting environmental rules like a jungle, swamp, icefield, etc?
Bottom line, for Me one of the largest factors in adding replay value to BattleTech has always been the environments themselves ... not the fluff, not a whole bunch of new mechs or whatever, but being able to go somewhere new and do something different.
You guys are doing a fantastic job, keep up the great work, and thank you for actually taking the time to ask Us what We'd like to see and for taking Our suggestions seriously!