I recently purchased vegas, and am coming from a job where i was on fcp, and cutting foley and music on soundtrack 2. I'm still getting used to the vegas workflow, and was curious how people were cutting looped music or foley work to their vegas projects. holla at me.
Vegas is so good at audio that you may not need anything else...seriously! I do all of my mixing and effects processing with it. It's fast, intuitive, powerful, and just plain sounds good.
If you do need more power for fine-tuning individual sounds, then Sound Forge is a good choice. I use it regularly for repairing waveforms; gotta love that pencil tool!
As far as looped music, you could throw some Acid loops onto the Vegas timeline, or create your own using Acid Pro which supports things like tempo/meter maps, midi recording/playback/quantization, softsynths, etc.
Me too. Vegas is great for audio. Sound Forge is used if some serious clean-up work is needed, or to concatenate narration (Vegas reads markers from Sound Forge, which makes cutting and editing in Vegas a snap).
Vegas also has a great looping feature which makes ADRing simple.