http://vulcan.wr.usgs.gov/Volcanoes/MSH/framework.htmlIndex with all sorts of good stuff, monitoring, maps, current hazard reports and so on.
Edited to add recent info from this page (listed on the index)
http://vulcan.wr.usgs.gov/Volcanoes/Cascades/CurrentActivity/current_updates.htmlInfo update from today at 9:20 AM PST
"Current status is Volcano Advisory (Alert Level 2); aviation color code ORANGE
Growth of the new lava dome inside the crater of Mount St. Helens continues, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. During such eruptions, episodic changes in the level of activity can occur over days to months. The eruption could also intensify suddenly or with little warning and produce explosions that cause hazardous conditions within several miles of the crater and farther downwind. Small lahars could suddenly descend the Toutle River if triggered by heavy rain or by interaction of hot rocks with snow and ice. These lahars pose a negligible hazard below the Sediment Retention Structure (SRS) but could pose a hazard along the river channel upstream.
Potential ash hazards:Wind forecasts from the National Oceanic and Atmospheric Administration (NOAA), coupled with eruption models, show that ash clouds that rise above the crater rim today would drift north-northeastward.
Recent observations: The volcano is clear this morning with only a small steam plume rising off the new lava dome. We plan to have vertical aerial photographs taken today in order to create a new digital elevation model of the crater and new lava dome. We also hope (contingent on availability of a helicopter) to get crews out today to do a gas-sensing flight and take oblique photographs."