| IME and IMO, plecos are NOT the best fish to obtain if the only goal is to control algea. My reasonings for saying this is that #1, plecos should not be kept on an 'algea only' diet and they do need supplimental foods as they get larger since they can eat algea faster than it can grow in most cases and #2, they produce more wastes that can harm water quality than they can effectively rid your tank of algea.
HOWEVER, I do not think that having one is a totally bad idea if you keep its high waste producing ability in mind and stay on top of water changes and regular maintenance. I also think they are cool and have one myself more for that reason than for any other. There are better ways to handle algea and I feel that the first big step is too keep a good eye on your water quality and keep your tank away from direct sunlight as well as limit the amount and type of light that you have on your tank. At any rate, algea is a fact of life though and I dont think any of us can say that we have never had some grow.
I really like to use A snail in my tank for algea that grows on decor since they can really get at the little nooks and crannies. I say A snail because many types can breed fast and your tank can quickly be over come with snails, leading to more stocking problems when trying to get them under control. I just feel that I would like to stock my tank with fish I want to keep rather than fish I need to do 'jobs' like control algea with snails or a pleco and/or loaches to keep the snails under control, etc... I also dont feel that it is too hard to get the algea off of the glass of my tanks and so I do not really worry about it a whole lot.
Yes, it is good to feed your pleco some veggies to help suppliment its diet. I have tried cucumber with mine but found that it liked zuchini better for some reason. The only problem I have had with this is keeping the veggies on the tank floor but I have found that the little lead weights that are sold to keep plants from floating work really well. I have also used a spoon stuck into the flesh of a cucumber/zuchini to hold it down as well. The biggest thing is to wash them very well since many of them could have pesticides applied or other chemicals to help them remain green and fresh looking while on the store shelves. I have also taken the skins off completely but this reduces the amount of time the veggies will stay in tact under water. Usually, once the pleco realizes that the food is there and he or she likes it (it can take time for them to eat it, so I would suggest offering it for a while even if it isnt being eaten), it doesnt last that long anyways. Of course, the other big thing is to take it out of the tank once a day or so has passed or before it breaks down completely and becomes another bio load on your tank. | 
Clown Pleco - Algae Eater or Not? 
