Corfu is a trully beautiful island so even a simple drive around the island is one of the nicest day trips you could do. Every coastline has something different to offer. The North has some beautiful drives up through remote little villages with spectacular views of the sea, the South has rolling hillsides covered in olive trees with long sandy beaches that remain quiet even in the heat of summer. There is also a pretty good local bus service on the island which is an inexpensive way to enjoy a day out.
Corfu town is always worth a visit. The evening is the best time when it is a bit cooler, it is a lovely town to amble around whatever your taste and on Tues, Thurs and Friday evening all the shops are open until about 9.30 with many staying open until midnight. Throughout the Summer there are also various music and dance events in the 'platias', fortresses, or music academy. Most of these are free or very reasonabley priced. You can get to the town by bus, car, organised excursion or by boat. There is also a regular local boat to the island of Vidos (a nature reserve and perfect for walking) which goes every hour through the Summer.
Being surrounded by crystal clear waters another perfect day trip is by boat. The North East Coast is stunning from the sea with a miriad of tiny shingle coves, some only accessable by boat. 'Nautilus' www.dailycruisescorfu.com is a beautiful motor yacht that does some really wonderful and good value for money trips along this coast with or without a fantastic fish barbeque. There are also little self hire boats for rent but be careful to check their safety equipment and insurance cover before hiring.
The North West is also wonderful to explore by boat with dramatic cliffs and amazingly clear deep blue water. Paleocastritsa offers several 'undersea' or glass bottom boat trips that are well worth while plus there are day trips on traditional 'caiques' plus some little boats that take you on a mini tour of into the caves which is a fun thing to do with the kids. Again there are self hire boats too but the sea can by choppy on the West and as always check safety and insurance.
Some sites that offer information www.allcorfu.com (bus time tables and restaurants) and TripAdvisor's Corfu pages and forums.
Corfu, and the rest of Greece, have so much to offer that one could go on and on about things to do and places to see. Pack your bikini, jump on a plane, and go and see for yourself....