Nuts! - one of my favourite sets of rules from Two Hour Wargames is their featured game this month. Which means you can get it for US$5 less than the usual list price - so the .pdf is only US$12.
All the Chain Reaction 2.0 based rule sets have a bit of a learning curve but once you get over that The reaction test system provides a different but very effective simulation. I've yet to find another set of rules at this level which gives you the "feel" that Nuts! does. It leans more to the realistic than the hollywood version of WW2 but that is what I was looking for anyway.