My youngest pair are into imaginary play, too... we have a costume basket that gets a lot of use...
Also have wooden train and legos... The train gets more use than legos here, but at my boyfriend's house, when his 6 year old plays woth my 7 & 5 year old, they play legos a lot...
Also games, Trouble, Don't Break the Ice, Don't Wake Daddy, were big hits last year... Now mine are older and like playing Upwards this week...
My 7 year old (girl) also likes her Carebear with a glow-patch on its stomach. Both my kids sleep with glow-in-the-dark stuff around them when possible, then we can turn off all the lights.
We also have parts of an Imaginatrex set- the dungeon pieces with trolls... there was a wizard's castle and knights and stuff that we didn't acquire before the pieces disappeared int he stores near us, but the dungeon pieces work well with the wooden train set, which also works with hotwheels and penny racers and dinosaurs and wild animal sets...
Oh, and I was going to suggest you get yours a pair of walkie-talkies and maybe an indoor tent thingy for indoor camping play. We have a lot of rain and such games are high on our winter list, even today. In fact, other games work nicely within the tent (or Scooby-car, or what-have-you...)