On your doorstep:
http://www.callendarestate.co.uk/things-to-do-in-falkirk/cycling-routes
Not challenging but you can ride your socks off as there 3 loops plus hundreds of miles of trails to and from the place / all over Falkirk.
You can link in with the Kelpies which is well worth a meander down to at dusk:
http://www.thehelix.co.uk/discover-helix/the-kelpies/
Slightly further afield (but very accessible via the Union Canal) you have Muiravonside Country Park:
http://www.falkirkcommunitytrust.org/venues/muiravonside/
No waymarked stuff but it’s small – just follow your nose. Some nice technical riding here and there – I use it a lot mixed in with other stuff.
Also Beecraigs which is now mostly waymarked and has some decent natural stuff:
http://www.westlothian.gov.uk/tourism/countryparks/beecraigs/Beecraigsactivities
Plean and Torwood are pretty limited in my view and need local knowledge. Ignore the comment above – Carron Valley is worth the (short)trip. Beast yourself up and down Meikle Bin (big hill / old volcano which dominates the area)if the waymarked stuff isnt enough. Fantastic views from the top.
Dumyat’s okay and worth mixing in with Uni Woods stuff. The out and back up the hill is simply a case of driving up and looking for the eroded path up to the top. North Third also good but needs local knowledge.
Polmont is a good base for the stuff I mention early on. Not sure on hotels though. Linlithgow also a good location as Beecraigs and Muiravonside are easily combined.