In re-reading some of the other posts I just have to say that y’all either don’t know squat about our legal system and laws or…nah, I got nothing else. Everybody look up the difference between an accident and a willful act or negligence. For example, Todd was completely within his rights to disarm Sheldon of his bat’leth. Sheldon had violated Section 417 PC of the California Penal Code. Of course, Todd then becomes a criminal by not reporting the incident to the police and turning over the weapon, but taking it was perfectly legal and justified.
Howard’s hair. I stand by what I wrote! 
Sheldon cut the power to the whole building in a fit of pique. Plus his emergency drills have to be disturbing the peace in some way.
And those “wildly carcinogenic” evacuation paths. Probably an EPA violation or something.
Moving violations:
In “The Love Car Displacement” Leonard is going 120mph (!) and a siren is then heard. Apparently Sheldon can tell that a police car has aluminum wheels. Just before this Howard threw a walkie-talkie out the window. Significant littering there.
In “The Explosion Implosion” Howard lets Sheldon drive his car. First, it turns out, Sheldon is not driving in either lane. Then Sheldon takes off and gets pulled over. He tells the cop he was going 112mph.
In “The Monetary Insufficiency” Leonard points out that Sheldon is driving a stolen car with a dead hooker in the trunk after Sheldon stops at a red light. 
Sheldon throwing Penny’s clothes on the power lines without the permission of their owner definitely brings some vandalizing charges into the equation.
As Priya pointed out, several clauses of his roommate agreement are illegal.
In The Einstein Approximation Sheldon stays in a mall store after hours and is caught by a security guard in the store’s ball pit. The guard doesn’t call the police because he was a nephew that is special, too.
Is soliciting prostitutes in Vegas a crime? I thought prostitution was legal in Nevada.
Prostitution is legal in *parts *of Nevada. Prostitution in Nevada - Wikipedia
In “The Peanut Reaction” Sheldon is at a Best Buy-type store and while getting a gift for Leonard he ends up acting like an employee. Including “breaking” into the sales system and placing orders. Even though “1234” is hardly a secure password, such actions violate Federal law.
In “The Irish Pub Formulation” Sheldon is playing a text-based adventure game (possibly Zork) using an emulator. The use of such emulators to play copyrighted games is a no-no. Some companies sue and since copyright violation is now a criminal matter there’s that as well.
Drug violations:
In “The Adhesive Duck Deficiency” Leonard, Raj and Howard eat some “enchanced” cookies. Illegal in CA at the time. While being unware that they were ingesting drugs might factor into a trial, a real hard nosed DA could still make their lives difficult. And Raj could be deported.
While buzzed, they get the munchies and Howard outlines an attack on a group of scouts to steal their food. While they didn’t actually do it, planning such a crime is a crime. Esp. with big doughy scout masters, couple cubs, mostly Webelos as their intended vics.
In The Plimpton Stimulation" Leonard says he didn’t get much sleep (due to Dr. Plimpton). Howard offers Leonard some of his mom’s sleeping pills. In passing he mentions that she doesn’t know she takes them. Not the only time Howard reveals that he secretly drugs his mom. The first action is a lesser crime. Secretly drugging someone on a regular basis with sleeping pills? That’s serious time.
In “The Bad Fish Paradigm” Howard secretly puts Valium in Sheldon’s milk.
Howard’s a jerk, if you get right down to it.
Sheldon also acted like an employee at The Cheesecake Factory, violting both labor and public health codes. The police would have called in about 30 seconds.
And he was guilty of public nudity in Howard’s car.
The conversation with the little girl at the library could have been totally misinterpreted. As Leonard put it “Walk out fast and don’t look at the security cameras.”
Dr. Stephanie Barnett told Sheldon he had an inflamed larynx when all she wanted him to do was STFU.
She also hid her malpractice of leaving an earring in someone’s body. And apparently she doesn’t even know the correct procedure for a cootie shot.
And Leonard knows about the “couple of fifties in Green Lantern’s ass.” Implying he’s taken some at some point (but probably replaced them).
IMHO, the top top crimes are destroying the elevator, and filling Kripke’s office with foan, both which could have serious consequences.
Amy gave Sheldon some “special, funny tasting, juice” to Sheldon to calm him down during their flight to Texas.
Was Sheldon guilty of assault when he threw a pie in Leonard’s face in his Mars video?
Penny got him drunk before his “Uranus” speech. And how many times has Raj been drunk in order to talk to women?
When Howard was up for the government job, they all committed some form of slander when talking to the government agent.
Unethical, but probably not illegal
I don’t think any of them actually lied, did they?
Except for unknowingly giving someone alcohol, none of these are crimes. And there was no slander. It isn’t slander if it’s true.