For the D3000 you will probably want something with AF-S unless you dont mind manual focus only.
If AF-S only, your options are limited in the prime lens market, really only the Nikon 35mm f/1.8 and the Nikon 50mm f/1.4.
If you dont mind manual only, then the 50mm f/1.8 and the Nikon 85mm f/1.8 are probably the "best".
Of course you could get a zoom rather than a prime, in which case something like the Nion 24-70mm would be fantastic, but at over £900 probably not very realistic.
Which leaves you with the 3rd party varients by Sigma.
I think Tamron have a highly regarded f/2.8 lens but I forget which it is, so Ill leave that to someone else.
Im sure there are loads of other AF-S zooms that are up to the job, but Ive never used them, so cant really reccomend them.
*edit* If going for the D90 soon, you might be better off considering the non AF-S lenses too, as the D90 doesnt need them, opens up a lot more choice