Whoa - what is up with all this spanking advice and support? I totally understand the frustration, but spanking makes no sense, especially if you are spanking him because you are trying to teach him that hitting is wrong! He will do what you do, not what you say.
I have a daughter who will be three in June, so I am in the same boat with the behavior. I see her experimenting with a lot of the same things your son is doing, and it is disturbing to see my daughter acting like she is enjoying acting like a little beast. I am a single mom, with little support, trying to run my own business. I really do get how hard it is, so I hope that you don't feel judged in any way by my response.
Your son is NOT a bad kid or a liar, but he IS doing this stuff for a reason. It sounds to me like he wants your attention - and he's getting it! If kids don't get what they want in a good way, they will settle for getting it in a bad way. So, the first step here is to chill out your reactions to his crappy behavior. The more upset you get with him, the more you are "teaching" him that this is a great way to get some attention from mama.
When my daughter's behavior starts getting way off track like this, I see it as an expression of HER frustration of not getting enough the attention and closeness that she needs to feel OK. I find ways to increase physical closeness with her (such as going for long walks with her in the backpack), and spending more time with her in ways that she wants (playing with favorite toys and games, etc.). Often, when I first give her this attention, she resists quite strongly and gets even more obnoxious. But I persist in a gentle, firm way, with a lot of humor and warmth, so she feels that I really do love her. At these times, I give her bad behavior NO attention, while still holding the limits (I physically stop her from hitting me, for example, but I do that by just holding her arm) and being loving, funny and warm. It is a tall order, I know, and there are times when I can't pull it off. But really - do give this a try. Once we are back on good ground together, I can talk with her about the stuff she is doing that has to stop. And THEN she gets it.
When kids feel unloved or disconnected, they tell us in the only ways they can. And no matter how much YOU know you love your son, there are times when he cannot feel that love. Those are the times when he acts like a little monster - think of it as begging for love with bad behavior. He does not need a big bad parent who will scare and hurt him if he does "wrong". That stuff is all about trying to control his behavior - and you will lose the control game every time. What he really needs is firm, loving limits and a strong sense of connection to you as the parent that loves him. The warm connection is what lets him accept the limits.
This stuff might sound all hokey and pie-in-the-sky, but it's the stuff that works best for my daughter, and also increases my confidence in myself as a parent. The few times I resorted to spanking left me feeling pretty crappy myself, and while they may have been effective in the short-term, the real problem never got addressed. My smart and savvy girl just figured out more dramatic ways to act badly and get the attention she needed.
Sorry for this long-winded response. I just feel so strongly about this, and some of the responses you received felt way off-track to me. I have found Patty Wipfler's little pamphlets on connection parenting really helpful. I got a set of them from Amazon - there are ones that talk about how kid's emotions work, how to handle tantrums and anger, etc. They are short, so it's easy to read them, and they get right to the point. She also has a website at handinhandparenting.org. I wish you and your family the best as you work through this tough stuff!!