You already have the P239 which is a perfectly good carry gun. It sounds like you are really looking for a home defense pistol. A full-size would give you a better sight radius and more controllable follow-up shots so it seems to me you'd be better served using your P239 for carry and buying a full-size as a dedicated home defense gun. Why do you want the second gun to be compact? Are you looking to trade the P239 to help pay for it?
Anyway, for what you are looking for (compact, concealable .40S&W pistols that have a light rail and can be used for home defense) there are several options.
-The SIG P229 as mentioned can be had with a rail and would be very similar to what you have and are used to.
-The CZ 75 Compact .40S&W seems to have a rail (
http://www.cz-usa.com/01.detail.php?id=63). I love my CZ 75B and can attest to their quality.
-If you like CZs and if you like polymer there is the CZ 100B, though it is far from the most popular CZ.
-I do believe there are a handful of 1911s available now with rails. There are also .40S&W 1911s out there. I don't know for sure if there is overlap, but it may be worth looking into whether you can find a 1911 in .40S&W with rails (or would you consider a .45ACP?).
-I know you said "price isn't an issue", but I love my Taurus PT140 Millennium Pro. It has so far been 100% reliable, it is well made, and it is quite accurate for a small concealable handgun. Mine (thankfully) doesn't have the rails, but most do now. Mine is so good that I would definately consider it over more expensive guns.
-With the quality of the PT140 M. Pro, I would also be inclined to consider the Taurus 24/7 if you want a larger gun.
-There are the Springfield XDs, now in several sizes so you can get that which works best for you. I've shot the full-size a few times when it first came out and I was very impressed.
-Of course there are the Glocks.
-I'm pretty sure both the SIGMAs and the SW99 can be had with light rails. The SIGMAs made today are good guns, if you don't mind the trigger. The SW99 is a much nicer gun, and priced that way. The SW99 is available in various sizes.
-I'm also pretty sure the Walther P99 can be had with light rails and it is made in various sizes.