My nephew was a biter at that age and it can be tough! My brother and sister in law had the same issues, but here is what they did:
1) Just watch him like a hawk. It's not fun, but anytime your child is interacting with other kids, you or his dad need to be RIGHT THERE and stop him before something happens to another kid. It was really hard- my brother and SIL missed out on a lot of 'grownup time' with friends and families, but it was the only way to catch their son before he bit or hit someone. They also called or sat and talked with their friends individually to let them know they were aware of the problem and tell them what they were doing about it. Their friends were concerned for their own kids- but were also very supportive of what my B and SIL were trying to do and felt sympathetic about it. You should not lose friends over this- they ought to understand that it is nothing you are doing personally or on purpose! If they have that big a problem with it, then either drop them as a friend or only spend non-kid time with them.
2) Watch your child closely. My nephew had a lot of 'tells' before he was going to bite someone. It often happened when he was tired or very excited and worked up. He would play 'harder' run around in circles, get more manic and he would get a definite 'look' in his eye- and then WHAM! My family -even the other kids!- just learned to really watch for that and when any of those things started up, an adult would take him off on his own for some quiet time to calm down. It was always made clear to him that unless he could play calmly, he would not be allowed to play. Again, this was sometimes frustrating for the adult, but it did seem to get the point through eventually.
3) My nephew was tested for all sorts of things, to make sure it wasn't a chemical issue. It was not for him, but if your son continues to be aggressive, you might want to look into that as well.
4)I think diet and TV are also huge for this. What is your son eating? Everyone knows not to give kids too much sugar, but get him off of processed foods and fast food and I bet you will see a change. Also, is he getting lots of physical exercise? When my nephew got a little older, they got him into a martial arts program and it has been wonderful for him. It is a combination of controlled physical exercise and mental and emotional self control and any good children's program will also emphasize respect for self and others. My son takes aikido and kids at our dojo start at age 5, but there are other types of martial art that start younger and you would be amazed at how positive it is for them.
Last but not least, he may grow out of it. My nephew was always much BETTER behaved with other people ( me, grandma, school) than around his mom and dad. He is a very bright child and once he got into a good preschool program that kept him busy, the problem went away.
He still had issues through age 3 and into 4, so it may take a little more time. He is still prone to getting over tired, but he doesn't bite or hit anymore! So hang in there and just be on top of him and hopefully he will also outgrow it!