A sentence should contain a complete thought. Once you finish your thought, you can finish your sentence, usually with a period. That makes your sentence more readable too. Yes, it’s legal in English to use conjunctions to put several thoughts into one sentence. But it takes a special kind of mind to follow the train of thought in a sentence that has two or three thoughts.
If you want to strongly emphasize a sentence, either because it’s emphatic or humorous, you may sparingly use a exclamation point. But use it sparingly! It’s supposed to express strong emotion. Don’t use more than one at the end of a sentence, unless you’re a strongly-emotional fourteen-year-old girl writing on MySpace.
The ellipsis seems to be one of the most alluring punctuation symbols, and I see it misused everywhere. From student papers to billboards to everyday e-mails and chat logs, the ellipsis is tossed in willy-nilly and often extends to four, five, or even six dots.