For improved signal you can get an N router. I won't recommend one particular manurfacturer as all of them are pretty good.
If you having trouble with wireless signal, why don't you try homeplugging it?
All it is, is a patch lead from your router to a plug that sits in normal plug socket and the room that has the PS3 or Xbox in, also has a plug with a patch lead connected to either the Xbox or PS3. It's basically a way of sending the internet through your mains electricity.
Have a look through
this lot. I think it could work out cheaper than buying a decent N router and N adapter.
Thanks to Zing for bringing Homeplug to my attention.