Lego is a great toy for 5 year old boys. They can spend hours building creations from their imaginations and then playing with them afterwards. My boy will build all kinds of things with lego sets, robots, cars, houses, different creatures, planes and rockets are some things he has built. You can buy specific lego sets which are designed for kids aged 5 years and up and there are lots of top offers on lego currently available from amazon.co.uk. Buy a lego city passenger plane reduced from £35.99 to £24.34 (aged 5 to 12). A lego city camper van reduced from £14.99 to £11.13. A lego city police boat reduced from £29.99 to £16.89. Click on the pictures below for these and lots more reduced prices.

Piranha panic game is a fun, quick paced game that 5 year olds will love. Get your fish to the top of the game but beware the marble piranhas can come and knock you out of the way at any time. Excellent reviews on amazon and an excellent price too , currently 
reduced from £16.99 to  £8.75.

I've just bought some Galt connect straws for my son. They also have good reviews and should keep 5 year olds occupied for ages builiding constructions. I love construction toys for this age group, great for occupying kids for hours and facilitating creative and imagination play.