The 64 is a good one. It works the route from the Termini to the Vatican. Handy on a wet day if that's where you want to go. Or anywhere along the line, which includes some key places.
Like the Piazza Navona, which in December has what is claimed to be Italy's biggest Christmas Fair. The rest of the year it offers whatever is appropriate to the time.
The Campo de Fiori is close by too, a really good shopping area. And keep an eye out for music programmes in the churches around there. It's a good way to get some high quality classical concerts at reasonable cost. Try the Chiesa di SS Biagia e Carlo which regularly hosts sympony performances.
Walk back along the narrow Via de Giubbonari. Beautiful individual shops, really quality. And not a plastic sign in sight. The window displays alone are worth photographs.
Back about the buses, €4 will get you an all-day ticket in the metrobus area.
