I have both seen for myself and heard some positive reports about fishing the Boise River through town lately. For those with patience, there are big brows to be found. In fact, this doesn't just apply to fly fishing. The days have been a little warmer and the water is super friendly to someone with boots and waders and a Saturday afternoon right now so don't be afraid to go exploring.
It's been years since I've been, and I haven't heard anything super solid lately, but Clear Lake near Buhl can be a nice fly fishing winter getaway. They don't stock as many fish as they used to here, but I understand they do stock some BIG rainbows. The water in this small lake is spring-fed and stays in the 40s constantly. If you bundle up on top, the water won't feel any colder below that it does in the middle of summer. It's fly fishing only and $10/day, you can call the golf shop at the country club to try and glean some info on the conditions before you go. http://www.clearlakecc.org/ If nothing else, they have a nice show pond where you can at least see trout and some old sturgeon swimming around. And the chicken bacon ranch at Pizza Planet in Buhl is the best I've had anywhere. Hey, it's not always about fishing.
I stopped by my local Sportsman's Warehouse recently and checked their big board of fishing reports. It sounds like there are trout and kokanee to be had by those willing to brave the chilly conditions at reservoirs like Lucky Peak and Arrowrock. You may be able to get a boat in the water and troll, but bank access is probably easier with the water levels where they are. At least you're not going to have a lot of competition out there.
As always, hope you'll stop by the site after you've gone fishing and share some tips with the rest of us. It'll be warm weather before too long, but we'll have some more ice fishing updates this month and next before that season is totally over.