Well, yes, the Boyne Valley is a must for the first time visitor.

*** Day one ***

Newgrange & Knowth via the visitor centre.

(these require your own transport)
Dowth
Fourknocks
The Hill of Tara
Rath Maeve

*** Day Two ***

Ask me to take you around the Dublin sites!
Kiltiernan portal tomb
Glendruid portal tomb
Ballyedmonduff wedge tomb
Kilmashogue portal tomb
Ballybrack portal tomb

(or if you want a full on day a bit further afield)

Punchestown & Craddockstown standing stones
Athgreany stone circle
Broadleas stone circle
Castleruddery stone circle
Boleycarrigeen stone circle

(or if you want to stay in the Boyne Valley)

Loughcrew