I don't know if you have this car seat (Chicco Keyfit) but if you do you could wait for the new Chicco Liteway Plus. It's a lightweight umbrella stroller that you can attach the Keyfit car seat too. I am getting this because I also have the Vista and I need a lightweight option and it will be versatile for me so I can either wear baby #2 and put my daughter in the stroller or my daughter can walk and I can put the car seat in the stroller. It comes out mid January.
As far as other lightweight strollers go, the Joovy Groove is a good one to look at in addition to what the previous posters suggested.