It depends where you are heading to in the Algarve.
If you heading to the Lagos end you could come of the A2 Motorway at Marateca, head down the old Lisbon Algarve road (IC1), turn right just after Messejana onto the N283 and follow the road through Odemira, (Country town) S. Teotonio, Aljezur (Small Castle) to Lagos. This is a normal 2-lane road with 90km/h speed limit and windy in parts but you will see a lot of the Alentejo.
If you are heading down to the Central Algarve, you could come of the A2 Motorway at Marateca, head down the old Lisbon Algarve road (IC1) and follow it all the way down to Albufeira. There are a couple of good restaurant/cafes to stop in Mimosa. My favorite is the first on the right running south. (Always forget the name). You could also come of at Ourique, (See: http://en.wikipedia.org/wiki/Battle_of_Ourique)
