The Hummingbird fishing-buddies are pretty decent and inexpensive. I have the 140C which has side scan mode and a color screen.
http://ca.humminbird.com/category/271308/Fishin%27_Buddy_SeriesI like the color screen, but it DOES eat a fair bit more battery power than the black and white one. I think the black and white model (120) will last twice as long on 4AA batteries (look at specs online or on box in the store).
The fishing buddy is great for anchoring up and fly casting. I'm sure this is what they're primarily designed for. You can turn the side scan feature on/off. I also use mine for slow trolling and it works fine. It is not suited for fast trolling as the "male end" of the finder (the transducer) will start to flop around in the female end that clamps to the boat. This is only an issue if trolling "fast." I've had no issues slow trolling flies, etc.
I love mine and have zero regrets buying it. The only thing is you NEED to figure out a good system with you batteries. I started out with a huge pack of AAs from Costco. When the 4 died I would just replace them. However I was going through a lot of batteries so I decided to go the rechargable route. I got a Sanyo Enloop package from Costco that has the charger and 12 batteries for only like 20 bucks on sale - a solid deal! When the 4 in the finder die I replace them with 4 spares I have on board, then charge up the 4 dead ones when back on land and put them back in the boat. I also carry the additional 4 batteries just in case I forget to charge up the other ones or whatever.
The fishin buddies are nowhere near the quality/technology as the big expensive ones, however for 200-300 bucks you cant go wrong. It's also nice that you can clamp/un-clamp then from your boat, use it on your pontoon or canoe, etc. I've had mine for 2 years and it's helped me learn new lakes better, find fish easier (esp when you can see the depth they're at!), and get into more fish IMO. There is a lot of tweaking you can do in the settings, esp with the side scan fearures, so RTFM (Read The F**ing Manual).