I visited Mount Saint Helens National Volcanic Monument during June, 2005. The first afternoon, I went in route 504 (at Castle Rock on Route 5) to the Coldwater Ridge Visitors Center and Johnson Ridge Observatory. Hummocks was a nice easy, simple trail without spectacular views. Coldwater Ridge to Coldwater lake was a decent hike but could be skipped.
The next morning I drove around to the South entrance and hiked some nice hikes, drove to the East entrance and to Windy Ridge before heading to Olympic National Park. The Trail of Two Forests is a very short elevated trail that I would definitely recommend. Lave flowed through a standing forest leaving holes in the lava where trees stood. I didn't have the desire to crawl through the lava tunnel (maybe 20 feet long) but it might interest some more adventurous types (when the wether is warmer.
June Lake was a very nice hike. Continuing past June Lake (the only hike of over a couple miles I took here) you have a very steep hike to above the height of the waterfall And Lava Canyon was another nice hike. The well maintained suspension bridge still swayed (not much at all but the feel was a bit disconcerting - it gives me something to build on when seeing the next moving with missing or broken planks and frayed ropes).