Now is the time to announce future asset sales - don't sell them now but give a notional date when we think the recession will be over when we intend to flog them.
The biggest asset sale currently planned is Ofcom's statement in Jan 08 that they intend to flog off a big chunk of Govt-controlled radio spectrum, 75% of which is allocated to MoD. Back then they said this could raise between £3bn and £20bn. All you need to do is cite the precedent of the sale of Chelsea Barracks (when all £950m of the proceeds went back to MoD) and Bob's your uncle.
Next on the list is Wellington and Hyde Park Barracks. Lovely central London locations and as far as I can see of no value in the defence of the realm.
Then as someone else mentioned moving bases to the North would save money - there's an entire episode of Yes Minister devoted to this proposal. Of course if there is evidence that these moves would significantly worsen retention rates in key trades then perhaps not.
Sadly my understanding re the bases in Germany is that we requisitioned all of the sites in 1945 and therefore if and when we hand them back we won't get a penny.