  We present four new exoplanets: HIP 14810 b & c, HD 154345 b, and HD 187123
c. The two planets orbiting HIP 14810, from the N2K project, have masses of 3.9
and 0.76 M_jup. We have searched the radial velocity time series of 90 known
exoplanet systems and found new residual trends due to additional, long period
companions. Two stars known to host one exoplanet have sufficient curvature in
the residuals to a one planet fit to constrain the minimum mass of the outer
companion to be substellar: HD 68988 c with 8 M_jup < M sini < 20 M_jup and HD
187123 c with 3 M_jup < msini < 7 M_jup$, both with P > 8 y. We have also
searched the velocity residuals of known exoplanet systems for prospective
low-amplitude exoplanets and present some candidates. We discuss techniques for
constraining the mass and period of exoplanets in such cases, and for
quantifying the significance of weak RV signals. We also present two substellar
companions with incomplete orbits and periods longer than 8 y: HD 24040 b and
HD 154345 b with M sini < 20 M_jup and M sini < 10 M_jup, respectively.
