Haftafish,
If I lived in Boise right now, I would spend 90% of my time on the Owyhee river (Oregon) below the dam for big hungry brown trout, there are some big rainbows as well the closer to the dam you get. Plus it's just over an hour's drive. Everytime I went there I caught at least a 22 inch fish and it's all catch and release so the fish population per river mile is phenominal. I used primarily big streamers and weighted pheasant tails. Although this stream is just over the border in Oregon, 95% of license plates are from Idaho. Open all year.
Number two on my list would be Silver Creek (Nature Conservancy). It's about a 2 hour drive, is a spring creek, gin clear, and has the highest density of trout than any other stream in Idaho. Bring a float tube, you'll see hundreds of trout swimming past you. Use flouocarbon leaders. Dries and nymphs. The mix is 50/50 browns and bows. Check regulations for season dates.
There's also the Big Wood river, just next to Silver Creek. You'll find some browns and bows here too, but with Silver Creek so close, why go here? Plus many of the prime spots are on private land. Often the water is really low and you see fisherman targeting vulnerable fish stuck in a hole, so I avoid this stream.
Then the St. Fork of the Boise. This is primarily a tailwater river, flows affect the bite. You'll find mostly rainbows, but they're gorgeous, and some whitefish with an occasional bull trout. I only fish this stream on a weekday, because it's very crowded. The fly you'll need most on the Boise is an elk hair caddis. If you go, make sure it's on a weekday.
Don't count on any reservoirs around Boise unless it's C.J. Strike. The farmers suck out every last drop out of surrounding waters. If you want lake fishing try Clear Lake. It's a pay to play FF only lake that's heavily stocked with rainbows. And the best part, it's only 10 or 15 bucks a day.
When temps are warm hit the Snake for smallmouths at Brownlee reservoir and C.J Strike.
Check the fishing reports at
www.idahoangler.com
and the Idaho Statesman newspaper every Thursday for updated fishing reports on rivers in Idaho. If someone can tell me how to post pics here, I'll gladly show you some fish from Silver Creek and the Owyhee. Fishing in Idaho is awesome to say the least, wish I was there right now. Good luck to you.