Therer are many lawn feeds on the market as you probably already know yourself. I woud go for one high in nitrogen, which will green up your lawn perfectly. "Miracle-Gro water soluable lawn food" is one that I have been using and found it to be very easy to use - and have had great results. What I also use is "Westland AFTER CUT". This is very good and can be applied straight away after cutting - (Granular). Doesnt need to watered in, and it does not scorch the grass...
Also think about Lawn sand which helps with the removal of weeds, moss etc and also improves drainage. This is also high in nitrogen.
Best of luck! 