I think the best bet for Tara would be working in / eventually running The Magic Box. It's a natural fit. But Willow? Hmmm. In past seasons, we've seen her affinity with computers and it makes sense that she could get hired on pretty much anywhere as a consultant/programmer. But then it hit me:
A Watcher.
She and Giles share many common traits; it's almost as if Joss & Co. are drawing parallels.
1. Rebellion and Magic
Giles was rebellious in his youth. Dabbled in magic, got in over his head, messed with forces he couldn't possibly control, and had to quit doing serious magic. We've seen this happen with Willow as well.
2. Research Geeks
Since S1, Willow has been Giles' right-hand person when it comes to research. If he didn't have the answer, Willow could find it.
3. On-the-Job Training
Willow's been there since Buffy came to Sunnydale. She's seen what a Watcher does, needs to do. How to train in mental and physical disciplines.
I can just see Buffy (or a new Slayer) coming into The Magic Box, late after patrol, getting info about the latest Big Bad from Willow while Tara helps them find the books/artifacts they need.
Am I just too damn sleep-deprived or does this make sense? And does anyone have other ideas on Willow & Tara's future (aside from getting married, having a daughter and growing old together)?