I have visited the surrounding of Windsor Castle in the Spring of 2013. It was perfect weather with loads of sunshine and no rain! (surprising for UK).
Getting there by public transport from London was quite easy as I though it will cost us a lot and take too much of our precious time. But I was wrong and I am happy I took my chance with this.
Windsor needs to be visited on a sunny day, possibly on a working day if you want to have the chance to get inside the castle. Otherwise you will have to wait more than an hour in the queue for tickets to get inside. (we decided not to wait and enjoy the good weather instead and walk more than 4km)
The pictures below (taken by me) will surely make you want to visit this beautiful city as soon as possible!