I am looking for a nice basic, but tasty vanilla sheetcake recipe. 

I need to feed 50 people, (with fairly generous servings!) and I would definitely do a double layer.

I can't use a doctored/extended box mix because I haven't budgeted for that, so the box mixes will be quite expensive (I'm in south africa).

I am tired of sifting through recipes wondering if they will work etc. So if anyone has a trusty recipe ? or can point me in the right direction? 

I also have quite a small oven, about 18" wide, so it is difficult to bake with big pans. I've posted a question elsewhere about my oven size issue if you could help me out !!!
http://cakecentral.com/t/754905/sheet-cake-in-a-small-oven