http://www.liveaquaria.com/product/p...25&pcatid=2725 - and in a 1.5 gallon tank you should not have algae, as you should be doing full water changes once or twice a week. I don't suggest putting anything else in the tank, but if you feel that you must, shrimp are the way to go, as they will not produce a whole lot of waste that will harm your fish.
Personally, if you feel the need for more living things in a tank that size, I would suggest a live plant. No.. they don't swim around and greet you when you enter the room, but it can be very rewarding to take care of them, and they do great things for your tank by neutralizing ammonia created by your betta. Your betta would love you for it. Just my .02.
Throwing in my .02 as well, you might want to know that it could end up very bad for either one or the other. Your betta might end up simply killing and eating the shrimp, or shrimp have been known to latch onto betta tails. In a smaller tank, I think the risk of death or injury to one or both creatures increases dramatically. I say keep your betta alone, and save up that money to upgrade his tank size, until you have a large enough tank to actually get him a couple of "buddies" and not have to worry so much.