As mentioned above, March isn't a great time to get to higher elevation trailheads. That said, there's plenty to do.
In Seattle itself: Discovery Park and Alki Beach Park (West Seattle) both offer nice views of the Sound. Golden Gardens Park in Ballard has an actual sand beach that is nice for walking. Somewhere I saw a map for a hike/walk in Queen Anne that connected all the stairways that looked like a fun urban walk. You could get to and from the start on the light rail to Seattle Center.
Downtown Mulikteo is quaint and walkable including the rocky beach south of the lighthouse. You can always find giant purple and orange starfish, watch kayakers, etc. The ferry to Whidbey Island is short (if you are driving onto a ferry at rush hour or weekend mornings, be prepared to wait, sometimes up to a few hours. There are special lanes for cars waiting to get on ferries. However, you can always walk on any ferry without waiting and for just a few bucks) and you can walk around Clinton.
A fun driving day would be to take the Edmonds-Kingston ferry, maybe have breakfast in Port Gamble, go to the 101 south, stop at Dosewallips State Park and walk on the beach (you can often see bald eagles there)and follow south. There's an decent hamburger place at Hoodsport (the main SE Olympic ranger is there). If you had time, you could start a quick out-and-back hike at Staircase into Olympic but check with the rangers about snow. Then either cut up to Bremerton and ferry back to Seattle or drive I-5 through Olympia.
For dayhikes on the east side, check http://www.wta.org. There's a clickable map under "Find a Hike". Look at the Mt. Pilchuck area for hikes that might be accessible. Or along lower Hwy 2 near Wallace Falls State Park.
FInally, if Dale Wambaugh doesn't see this thread, you should PM him.
Good luck and bring a rain shells!