Oscilloscope is one of most important test devices in electronics. If your needs are not very high, you can go with any cheap or DIY scope. But in the end I would recommend getting standard bench oscilloscope. It saves time and eventually money. If you currently have low budget for purchasing scope, then take a look at this following scope project where vaupell builds it with Arduino Mega and TFT display.
Scope project is mostly glued out of two sources where one deals with Arduino scope functionality and another with TFT display. The end result looks great and serves the needs.