I have a nice small little Sony one which works fine on the DART (and everywhere else - only frequent loss in signal is entering the tunnel at Kent Station, Cork), don't have it at hand so can't give the model number but is about 16 months old so probably a bit outdated now.
Went with as basic a model as I could. Manual tuning wheel, no presets etc. as I was more interested in a good battery life (though, from experience, the tuning lock mentioned above by Murt would be a huge benefit as the station can get lost with the wheel being hit in a pocket) than too many options.