You can very easily do a store wide discount if that's what you're looking for. One of the nice things (although coupon codes would be a whole lot less hassle I'm sure so everyone is still waiting on them) is the Grid. Have you played with the grid at all? It's pretty amazing in itself. I haven't used it in quite a while so I might be rusty on how it works exactly, but I did use it intensely for a year or 2 and it's very easy to copy and paste something into an entire grid section.
What this means for you is that you can find the column(s) that represent the discount area which ususally comprise of the percentage of the discount OR a dollar amount, whichever you prefer.
PLEASE MAKE A BACKUP BEFORE YOU DO THIS IN CASE IT TAKES A FEW TRIES TO GET IT RIGHT FOR PRACTICE SO YOU CAN ALWAYS GO BACK IF YOU NEED TO.
1. Enter that discount amount into one of the products as you normally would to make it show up in the Grid so you can find it in the grid easier.
2. Open the Grid and look for that particular column.
3. Copy the box that has the discount amount in it
4. Click the Title bar of that column (same as you would for Excel if I recall) or drag and highlight the entire column, whichever works.
5. Now Paste that discount you copied and it should copy to every single product's discount setup.
As I said it's been a while, but that should be the basic setup for it, you may need to play with it just a bit if I've missed something, but it shouldn't be too hard to do.
Once you have done with your sale, just go back to the grid and highlight that column again and delete the info there and the discount is now gone from all products.
Hope that helps