There are several types of repeals.
First, there are partial repeals where a poorly crafted portion of a law causes problems. For example, the onerous 1099 reporting section of the Patient Protection and Affordable Care Act (aka Obamacare) was repealed. The rest of the law remains intact so far but that portion was repealed. Another recent example would be how the Patriot Act (2001), the Terrorist Surveillance Act (2006) and the Protect America Act (2007) effectively gutted provisions of the 1978 Foreign Intelligence Surveillance Act.
Next, there are repeal and replace laws. In some cases, a previous law is explicitly repealed and replaced with another law. In other cases, the law is implicitly replaced and rendered moot without it being formally repealed. This has been done many times. One recent example would be how the Great Depression era Glass–Steagall banking acts were implicitly and explicitly repealed by various acts, most notably the Gramm-Leach-Bliley Act of 1999.
And, there have been outright repeals without a replacement. In this situation, a law or regulation is repealed and the act does not contain any replacement law or regulatory authority. One recent example would be the Don't Ask, Don't Tell Repeal Act of 2010. Another example would be the repeal of laws prohibiting private ownership of gold bullion by US citizens. Sodomy and 'blue' laws have been another common area where laws have been repealed without replacement.