For final output, you are usually fine saving as .jpg. (use highest quality). Saves on disk space, and makes it easier to share your images with anyone.
After your initial conversion, you may consider making that your "master" copy (keeping the RAW as your "negative" too), and then only working on a second copy, that way you have an original to go back to.
If I have alot of edits, I'll save as .psd (photoshop format) so that I preserve my layers, and I could go back in and adjust them.
It really all depends on how concerened you are with preserving edits, and what steps you want to add to your workflow. (and everything etaf said too.)