Lisbon sightseeing Grayline proved great value at 20 Euros for a 2 day ticket; they have 4 lines altogether, the Red Line being the main one for the city sights. The Green Line is the one for castles while the blue line takes in the outskirts of the city. The orange line will take you along the Estoril coastline and into Estoril itself. The latter line runs only hourly so set off by lunchtime if you want to have time to stop off at the coast. The other lines are very frequent; 15-20 minutes. Your ticket will also get you a free ride in a tuk-tuk; obviously not the hour you get with the commercial tuk-tuks at around 45 euro but I got a good 20 mins and it cost nothing at all.
There is free Wi-Fi too if you want a quick catch up on emails or social media.
They have a facility for wheelchairs, but I am unsure how well it works if boarding from any stop other than the main town centre one where all tours depart from as access is via the back of the bus.
This really is the line to go for if you want to get the most from your sightseeing; I was very happy indeed and got to see loads in the four days I spent in the lovely city of Lisbon