Need Suggestions.

[ToogiiK]

I was thinking about selling/trading my 28-135mm for 430 exII, and have my kit at 50D 50mm 1.8 with the flash, do you think this is a good idea?

[eyalg]

A 430EX flash is a very good idea, it will allow you to be much more creative in many more situations.
However, selling your 28-135mm and staying with just a fixed 50mm lens means you'll be very limited focal range wise.
If you really want the flash and can't afford to just buy it without trading the lens for it, then you could also get a 18-55mm in order to have a nice all around lens for day to day use.

[MrJones]

I don't think that staying with just the 50mm is a good idea.
the funny thing is that with the f/1.8 you'll hardly need the flash