What tidal databases are available to be used as model boundary conditions?
The boundaries to coastal models are frequently forced using information on water level (or, less commonly, velocities) predicted from databases of tidal constituents. These databases may be global or regional, and typically they offer a grid of points with constituents available at any of these points. 

The products listed below are all produced by global tide models informed by satellite altimetry. All will give water levels, and some will also give depth-averaged velocities. As with any global tide model, caution should be exercised when applying them in coastal and/or shallow water regions, as they are unlikely to have the resolution (of bathymetry or computational mesh) to resolve coastal effects.

OTIS

One source is the outputs of the Oregon State University Tidal Inversion Software (OTIS). OSU host a number of different data sets which are accessible from this page, along with the software required to extract constituents in FORTRAN or MATLAB. Both global and regional grids are available. The data here are based on TOPEX/POSEIDON satellite altimetry, combined through data assimilation techniques with a basic global tidal model and, in some cases, coastal tide gauges. The various grids have varying resolutions and varying numbers of tidal constituents.

DTU10

Another source is the DTU10 model from the Technical University of Denmark. This information is produced from a global tidal model combined with TOPEX/POSEIDON data and also Jason-1 and Jason-2 satellite altimetry. The model is described in a poster here. This model has a resolution of ${\frac{1}{8}}^{\circ}$ and includes twelve tidal constituents. Use of it is likely to be widespread in industry because it is included in the commercial modelling package MIKE by DHI.

FES2012

The newest dataset listed here is FES2012. More satellite data was used in its building than the other two models listed, and an improved model was used. The authors claim especially good performance in coastal and shelf regions.
Data are available on a ${\frac{1}{16}}^{\circ}$ grid with 32 tidal constituents.

NB: this description is based on the linked web page. I have not personally used this dataset yet.

Regional databases

In order to minimize the effect of applying a global tide model solution to coastal and/or shallow water regions, regional tidal databases are available. Some examples are:


As mentioned above, OTIS provides a number of regional databases around the world with varying resolution (from 1/12 to 1/60 degrees).
ADCIRC tidal databases: One encompasses the Western North Atlantic, Caribbean and Gulf of Mexico (up to 60W); and another one the Eastern Pacific (from Alaska to Mexico).
Many examples of local tidal model simulations are available for many specific locations, but the solutions are rarely available online.


Other sources of boundary data

All of the above data sources provide surface elevations from models. In the near future it may become feasible to produce velocity boundary conditions from land-based radar measurements of surface velocities in some areas.