I dedicated a few posts recently to covering the transition of BAA WorldPoints to Heathrow Rewards. The scheme is now only valid when you spend money (on pretty much anything) at Heathrow.
The old BAA WorldPoints scheme always had a number of decent sign-up promotions, and the first one for Heathrow Rewards has now appeared. The sponsor is British Airways.
In summary, you will receive 500 bonus points (= 500 Avios) when you join Heathrow Rewards via the BA link and spend £30 at Heathrow in one day before 30th September.
We have seen more generous offers than this (I think there was 1,000 points for a £10 spend last year) but this one is not bad. Remember that Heathrow Rewards now lets you transfer points to other people so you could get an account in a different name and merge the points with your own.