I have three ideas for episodes that I personally think are good.
1: The Nintendo Epidemic
When Raj first came to America, he had an Indian disease, but his people have a natural immunity. It ends up on the guys' Wii. Sheldon, Leonard, and Howard are get sick, and then the disease passes to Bernadette and Amy. While the five are trying to recover, Penny gets a job as the main character on a new TV show, and somehow Raj convinces her to let her be her manager.
2: The Foster Child Hypothesis
After some budget cuts at the University, and their pays lowered, Howard, Raj, Leonard, and Sheldon take in two twin foster girls. The children are really annoying and troublesome. The children even erase Sheldon's work, so he convinces the others to give up the kids.
3: The Doctor Wolowitz Experimentation
After years of being tormented for not having a PhD, Howard is pushed over the deep end when he is denied a promotion at work for not being a doctor. Howard goes back to college, and Sheldon heads after him to make sure he doesn't fail, so he gets the promotion, so he can pay back a loan from years ago. Sheldon ends up getting a MD in Engineering somehow.
Any suggestions, or your ideas for episodes, you can post if you want!