Day trips from Melbourne

My recommendations would be Marysville, Wilsons Prom, Sorrento, Lorne. Pretty much what everyone said, they are awesome places to visit & chill out.

In weather like today, a drive to Lakes Entrance and visit the Buchan Caves, should be nice and cool down in those caves :)

Winchelsea just outside of Geelong has some awesome junk/collectors shops to trawl through. You could browse them while on the way to the most amazing of all lunch experiences at Sunnybrae in Birregurra, so you get your fix of trash and treasure then your DH gets the benefit of a beautiful lunch with your company - win/win! ;)

Sunnybrae is a farm/restaurant in Birregurra where they only do one sitting for lunch with a set menu (few little options) using local ingredients and their courtyard brick oven. It is a 12pm to 5pm sort of thing, eat all day and take a wander around the property, vegi garden etc between courses or browse their amazing collection of food/cookbooks while enjoying the serenity. It is my Number 1 choice for a day trip at the moment.

I wouldn't do East Gippsland as a day trip - too much to see and do and it takes a good 3 hours at least to get there from Melbourne. I don't visit my parents unless I can get in two nights minimum. It's such a mindnumbingly boring drive that I have to have that break in between!
Meanwhile, once you're there, that whole region is a goldmine :)
I've just been reading my copy of Gippsland magazine and I've got some ideas for heading out for one of the nights with just DP and I, so that the kids stay with my folks till bedtime. Bruthen is a town I have been dying to explore (we only ever drove past it to get to Buchan as kids). Metung is a nice place but a bit overrated, I feel (and my parents lived there and still have a vacant block there). Rail Trail, wineries, kayaking, boat hire on the lakes, fresh seafood at Lakes Entrance...I do love that area :) Not a day trip, though.