While perusing TMP recently, I also discovered a free set of ECW rules called "For Parliament, King or Glory" and written by David Marks here. You do have to join a Yahoo Group to be able to download the rules, but that is relatively painless as it doesn't require a waiting period or moderator's approval, your application is auto-processed and there you go!
These rules look quite promising and should very easily transition into the post-ECW period. They should work especially well for the Anglo-French alliance against Spain (with English Royalist and French Rebel assistance) in 1658 and 1659. I think they would also probably work with minimal mod's well into the later 17th century. I will warn you before you open that pdf file and just click print however, the rules are very detailed and are some 80+ pages long, plus the cover and QRF sheets.
They appear similar in some ways to "Beneath the Lily Banners", as they use the seemingly "standard" of 3 bases equals one battalion format. The mechanics look well thought out, there is a wealth of detail contained within the rules, but it looks like a game can be played with just the QRF sheets once players are familiar with the mechanics. There are also some excellent optional rules, army points values, and appendices with a chronology of the ECW, Commander ratings, gaming counters to reflect unit status and other important facts, and a very nice means of representing variable pike to shot ratio's for individual units.
After a read-through and a few "pencil skirmishes", I feel that these may be a very playable set with excellent expansion potential. Has anyone else tried them yet? Your thoughts or input?