I'd say get a flash, and then that opens up your options for lenses. For example, the 430exII flash is like, $250, that gives you $750 to either get 2 primes or 1 good zoom that covers that range. Because any f/2.8 lens, indoors, won't get you the shutter speeds you need to shoot anything other than people standing still (unless you go ISO1600+).
I just shot my friends wedding this past weekend, so there were multiple indoor rooms with only sunlight from outside helping lighting. Without flash, I'd have been shooting at 1/30th shutter speeds and ditching 90% of the photos. With the flash, I was shooting at 1/160th and 1/200th, which means I keep 90% of the photos. And this includes the 50mm f/1.4 I shot with, I was lucky if I got 1/80th shutter speeds at ISO800, and that was only when pointing at the windows. And if you're indoors, its really easy to bounce the flash to create nice lighting.
Otherwise, I'd say consider the Rokinon/Samyang lenses that do f/1.4 if you can accept MF, if not, then I'd say your options are the Sigma wide-angle primes (20mm, 24mm, both f/1.
or the Canon 28mm f/1.8. I think the Tokina will be too wide for general use.