I know there are groups trying to preserve parts of the London South Western and Midland Joint (a.k.a. the Somerset and Dorset) near the Bath end of the route—running into trouble I think because much of the unbuilt-on route is cycle track now.
There is actually quite a bit happening at the moment:
1) Midford is being restored by the New S&D as an information point. Site clearance is virtually complete now and plans are about to start being drawn up once things like underground water pipes have been accurately located.
2) Midsomer Norton (which is looking fantastic now, by the way) are currently extending south towards the (infilled, unfortunately) Chilcompton cutting. Northbound there's a missing bridge immediately adjacent the station, but from what I've heard that might not actually be an insurmountable obstacle in the medium term.
3) Shillingstone have a new signal box and have just had a tracklaying binge - they now have about a tenth of a mile of track laid in the southbound direction (coexisting with the trailway). It's been really quite inspiring to watch their progress (they're posting very regular updates on Facebook) recently.
4) Things might be about to start happening just south of Blandford. Watch this space.
As if that lot isn't enough it looks like the S&D Trust at Washford on the WSR is going to be looking for a new home within the near future. Anyone care to bet it won't be on an S&D site this time?