Depends where in Wiltshire you are:
North Wilts- I take it you've tried Spirthill- pretty tame, but quite fun, plus lots of quiet lanes to get there including some huge climbs if you're into that. Lots of short bits around me- Box woods is great for big drops and gnarly tree roots, but very short, although there's lots of variations. Also lots of small sections of bridleways and woodland trails nearby which link up.
If you're further South in Wiltshire you've got Salisbury plain, and the Fosse Way runs right across the county.
For days out I tend to travel across the bridge to the Forest Of Dean, not too far but lots of variety.
Wanted: Bontrager ti-lite frame or bike, medium