I have been solely relying on Rome2Rio (click the link for a quick explanation of what Rome2Rio is) for planning transportation around Europe. However, only recently have I noticed that it doesn't provide complete information. For example, some TGV routes aren't included and I've had to find routes through other websites. Are there other websites similar to Rome2Rio or is there a more complete version of such a site?
I'm Chris from Rome2Rio, if you don't mind sharing your experience we'd be keen to find out which TGV routes and European routes in general you have found are missing from Rome2Rio results. This would help us review and improve our results in future. If you prefer you can send the details to firstname.lastname@example.org
If you are looking for alternatives to Rome2Rio you could also try routerank along with the Voyage SCNF site already mentioned. Also there are a couple more German focused sites with similar concepts GoEuro and Waymate in the future they may expand to feature other European countries in their data.
Some other sites that you may already be aware of that I'd recommend would be Bahn a comprehensive schedule planner along with Seat 61 which has good references and guides to travelling by train in Europe.
There also several nice sites using the Rome2Rio API, but as it is generally the same dataset as Rome2Rio you may not be as interested in those :)
I think adding GoEuro for europe is important, specially because you can do booking. Note that I work for the company.