Much like March 2008, April 2008 was cooler than any month in the 2001-2007 period except for July 2004.
Commercial break: an unusually balanced article about polar bears in Time magazine...Between March and April, the Northern Hemisphere cooled down by 0.06 °C (remaining anomalously warm) while the Southern Hemisphere warmed up by 0.06 °C (remaining anomalously cool).
RSS MSU: 1997-2008. Click for more graphs.
The fastest warming in that period, by nearly 1.0 °C, occurred between 70°S and 60°S - the Southernest strip they measure, and in the continental U.S., by 0.6 °C. The 20°N-20°S tropical strip has warmed up by about 0.05 °C, too as La Nina is weakening, converging towards neutral ENSO conditions in a few months.
John Reynolds has pointed out that UAH MSU has released their new satellite results, too. And they are rather different. April 2008 was 0.074 °C cooler than March 2008. The Northern Hemisphere cooled down by 0.25 °C.
The most significant difference comes from the tropics. While RSS MSU announced month-on-month warming, UAH claims a 0.04 °C of cooling, leading to the anomaly of -0.531 °C, the coolest reading since March 1989.
HadCRUT3 confirms UAH's 0.07 °C of cooling between March and April.
GISS plus sea surface temperatures, managed by James Hansen et al., reported a much larger 0.21 °C cooling between March and April but you should appreciate that their March reading was insanely hot so they just return closer to the trend lines observed by other teams.