With all negative implications of "cheap"...

There is PC software that allows you to use your sound card as an oscilloscope. Just type "sound card" "oscilloscope" and you'll catch quite a few hits. It can do up to 44MHZ, but the bias and gain reliablity is as good as none. Also most of cards have built-in high-pass filter so anything below some 5HZ gets lost, and DC signal is always shown as 0.

Advantages? It costs very little and works in most cases.
For professional work I recommend professional tools, but if you're just a hobbyist, it may suffice for a while.