I already have the TransG (hurr). Are IG and TG any different?
Industry Giant 2 is kinda more of the same sort of thing but with more goods, more control on what's made and having to sell goods in town. If your in love with Transport Giant then it's worth a look.
Traffic Giant is planning the transport route through cities like Cities in Motion.
They are different and worth a look if they're the kind of managerial games your in to. Some youtube video's might explain things better than me. I've played so many of these types of games and get confused with what's what.