With your own car (I posted this on another thread for Janine100 but thought it would be better on a thread on it's own rather than buried in one on newspapers ;-) )
Here's a few idea's for when you venture out in the car.......a good day trip is to head up to the Lassithi Plateau. If you head back on to the National Highway towards Heraklion at I think it's the first roundabout (but it is sign posted) take the left and head towards Mohos and then up to the plateau. When you reach the plateau itself turn right and then you can drive round the circular road exploring many villages along the way. The reason I say turn right is this will make your first stop the The Dikteon Cave but you will end up back where you started. When heading back take a detour to Krassi which is a lovely village and from there either take the same way back (stopping to explore Mohos) or the way back signed Malia from Krassi.
If you just wanted a late afternoon drive then drive to Malia (5 mins) and at the first main junction on the main street turn right (again sign-posted) towards the Plateau, stop at Kera for a drink or meze in one of the taverna's and have a look round a lovely handmade gift shop. It's only about a 20 minute drive and the views are lovely, you can also visit Krassi and the entrance to the plateau is only 5 minutes from Kera.
Another idea for a day trip is to head towards Ag Nik but turn right at a main junction just before you reach Ag Nik and follow the signs to Krista, as you enter Kritsa turn right and follow the signs to the ancient city of Lato which is only 3/4 KM along the road. Then head back to Kritsa and drive up to the Katharo Plateau which is a lovely drive. On the way up there is an old rickety picnic bench with amazing views and there are also a couple of taverna's when you reach the plateau. Afterwards head back to Kritsa for a stroll round the lovely village and try and track down the house where the "daughter of Kritsa" lived (I can give directions though ;-) ). There are also some nice roof top taverna's with great views if you are in need of refreshments ;-).
A day trip to Spinilonga is another amazing day out (I'll post an idea for that later....or copy and paste and older trip report....I know Lazy Jock ;-) ).
For shorter drives from Sissi you have Epano Milatos (a lovely traditional village) then venture up to Milatos Cave before heading to a lovely tavern at Kounali.
Another short drive is up to the lovely mountain village of Vrehassi (with a traditional house museum you can look round) just head out of Sissi in the main road and at the T junction turn left and just follow the road before veering left and up the mountain road to the village.
The Moni at Selenari is only a few minutes drive away as is the ruins of Malia Palace......okay my fingers are now cramping up which tells me I have rattled on long enough but any other questions just ask away :-)