Scope 100mhz dual trace is a good recommendation. Ebay has Tektronix scopes going all the time, look at the 465B. I paid up to $10,000 many years ago for some of the Tek scopes that are now going for $150. Tektronix makes great scopes. You need two traces to compare one signal vs a second in correct time relationship. This is especially true when working on digital circuits. Now if you truely want the ultimate, get a digital 4 channel Tektronix. Digital scopes will capture one time events, and allow you to evaluate what happened. Logic probe, yes, great troubleshooting aid. But if your dabbling in electronics, build your own. A real good 4 1/2 digit dmm is another excellent investment. Accuracy in resistance and voltage measurements can be a real lifesaver sometimes.