Don't get me wrong -- I am not suggesting that the 48GX is superior to HP's current models. I bought the 48GX several years ago, when it was still the top of the HP line. I upgraded it with memory cards, Java, Erable, Alg48 etc. and it's worked out fine for me. Since I'm basically satisfied with it, I don't have a compelling reason to upgrade to a 49G, 48GXII, or 49G+.
But if I had to replace the 48GX today, I would most likely get an 49G+ instead. A used 48GX is probably in the $150 to $200 range. I have 128KB and 512KB memory cards from Cynox; the combined cost is currently 93 euros, or about $115 plus shipping from Germany. So it would probably cost some $250 to $300 (or more) for a similarly-equipped 48GX today.
That's twice the cost of a brand new 49G+, which is in the $130-$150 range. And the 49G+ is much faster, has 2.5MB of memory, an SD card slot, a larger display, and flash memory upgrades. And all the software improvements are preinstalled.
I suspect that the 48GX is more attractive and has a better keyboard; don't know for sure since I have not actually seen a 49G+. But I also expect that the appearance and keyboard of the 49G+ are at least adequate. Given the lower cost and other advantages of the 49G+, it seems like the better choice today. I suspect that if I actually tried one, the old 48GX would seem impossibly sluggish in comparison.
If you want to do general scientific or engineering number crunching, then any 48 or 49 series calculator will be fine. But if you also want to handle symbolic math, then you are probably better off getting a newer model like the 49G+. You can add symbolic math capability to the 48GX, but you will pay a lot more for less memory and slower performance.
Actually, if I was starting over today I might choose the 33S. I originally got the 48GX for use on the NCEES engineering license exams. All 48 and 49 series calculators have since been banned on these exams.