I have a 50mm 1.8 is all... Im getting into on camera/ Off camera flash and strobist work. I shoot mostly portraits and do majority video
And my budget will be 600 USD
So, if you're doing portrait work and video, then you are probably going to want to aim for primes. Going the 15-85, 18-135, etc dont really make sense unless you were doing travel photography.
There are basically two ways to go
1. Go all primes. So, maybe the new ef-s 24mm lens as well as the 85mm f/1.8 (or 100mm f/2). That would cover most general portrait work, and if you needed wider than 24mm, then something as simple as the 18-55 kit lens may do it.
2. Buy a 17-50 f/2.8 (if Tamron, I'd go non-VC) and then get another prime (85mm/100mm). That'd cover you from 17-50 and give you a closer portrait lens as well.
Ultimately it depends what kind of video you are doing. If you're in constant motion, then you'd probably have to grab primes or zooms with IS to make up for that, but if you are shooting locked off, you won't need that.