The main ones are -
The Blue Dog Coalition - made up of fiscally conservative democrats. Currently it has 52 members.
Progressive Caucus - the 'progressive' group which has 78 members. Their positions are set out here.
New Democrats Coalition [NDC]- the moderate, pro-growth group which has 64 members.
Membership of these ideological groups is not exclusive - Andre Carson; Jim Moran; Jared Polis and Laura Richardson are members of both the Progressive Caucus and the New Democrats. 21 Blue Dogs are also members of the NDC.
There is also the
Congressional Black Caucus - with 41 members.
Congressional Hispanic Caucus - with 23 members.
Congressional Asian Pacific American Caucus [CAPAC] - with 12 members (one of whom is a Republican) and a number of associate members.
These groups do have some members in the Senate.