Oh man, OllyDbg was excellent. I was never great at reverse-engineering, it was mostly a "change random jmps and hope it works" thing for me, but it was exciting. Nobody I knew had credit cards back then, and I was a teenager, so I couldn't pay anyway, but I'd get shareware I don't use just to see if I can crack them. I'd delete them afterwards.

I once created an "uncrackable" crackme (in Visual Basic 4, no less!) that had a part of its code encrypted with RC4, and the license key was the decryption ley.