Hi Y.,
He may be teething--my daughter is close to his age and generally very sweet-tempered, but she has had bouts of irritability lately because she is cutting teeth (the first just broke through a couple days ago). Try Hyland's teething tablets--they are homeopathic, no side effects and they work like a charm, she calms down right away! You can get them at Whole Foods or Central Market.
He might also have a tummy ache or something--if the teething tabs don't help you might want to check with your doctor. Another possibility is a food allergy--if he is starting solid food he may be allergic to something he ate. My daughter had corn a couple weeks ago and it didn't agree with her, she was irritable and didn't sleep well for 2 days. When we cut out the corn she was fine again within 24 hours. Our doctor recommended introducing one food at a time and staying with it for at least 5 days before introducing the next thing, so we could tell if she was reacting to it--it's been a good method.
Don't ignore him--babies under a year old don't throw "tantrums" the way toddlers do--when they are upset there is something wrong and hollering is the only way they can let you know, they don't have any concept of trying to manipulate you like an older child will try to do. When he gives up crying when you ignore him it is a depressive response, he's getting the message that his needs are not going to be met and withdrawing into himself. When he is older (12 months and up) and starting to talk is the time to set the boundaries because that's age-appropriate, but now he needs your attention. It's rough, I know! But you'll get through it and even if he is really cranky, the love you send him by staying with him through it now will last him the rest of his life.
Best of luck--let me know how it goes!
C. :-)