First, you need to exactly identify the kind of algae you have: hair, brush, thread, staghorn, etc. This is very important. Most algae eaters eat only one or two types of algae. For example, otocinclus will eat mostly green encrusting algae, plecos prefer brown algae, and Siamese algae eaters will consume hair and red algae.
If you do get a pleco, do NOT get a common pleco. Get a bristlenose or other species that remains small. There are two reasons for this:
1) Common plecos get absolutely huge
2) As they get larger, common plecos actually stop eating algae and become mostly carnivorous. Not good for keeping your tank clean.
One of the main culprits of algae buildup is nutrient imbalance. How often do you do water changes? Too much nitrate is a big cause of algae. Also, you may be letting too much light in the tank.