For spray on primer I use regular spray paint. I buy it at Wal-Mart for $1/can. For Varnish I use DullCoat from Testor's as well as the Vallejo brand.

I've used Army Painter's sprays before, but  ended up buying GW's black spray since my FLGS had ran out of both AP and Vallejo last time I was there. The GW one is a tad more expensive but I actually find it to be better than AP. 

As for varnish I just use Army Painter's Aegis Suit, which is rather nice. 

I use spray cans of matt black and matt white from Halfords (UK car accessories store for those not in the UK) and Humbrol spray matt varnish from a local model shop.

I prefer to hand apply everything as I have had some nasty experiences with sprays, particularly matt varnish (frosting - where the varnish leaves a semi-opaque white layer over the figure). For undercoating I use Vallejo white primer, then apply Vallejo black over that. For varnish I use a couple of layers of either Vallejo or Winsor and Newton acrylic varnish. These have the advantage of never frosting and never yellowing over time.

If you get frosting using sprays, a second coat will fix it - at least it always has for me.

Nothing wrong with hand applied primer and varnish but for me life is too short when there are faster and easier alternatives.

Each to their own though.