The original 802.11b "AirPort" cards that Apple shipped seemed to have a strictly finite lifetime. I bought two in 2001 - one I put into my wife's Powerbook G3 Pismo, and one I bought installed in a then-new Powerbook G4 Titanium. Both died within about 3 months in 2004 - they still look OK to the software, but they no longer make any radio contact (so it looks like your basestation is missing - it took me a while to realize what was going on, but remember, for about 3 months I had one broken card and one working one, so I could try swapping them).
When I was sure my first one was dead, I called Apple. The card wasn't covered, but I thought maybe I could get it repaired for less than the cost of a new card. No way! Not only was replacing the card the only option, but the original AirPort cards are no longer available. The Apple tech I spoke to suggested looking on eBay. Given the finite lifetime of my cards, buying a second-hand one seems like a bad option, particularly since they command prices even higher than when they were new, due to the limited supply.
Now, you can get 3rd party Wi-Fi cards pretty cheaply, but they all involve the antenna sticking out of the side of the PC card slot, much less elegant than the built-in antennae of the powerbooks (although the internal antenna of the Titanium powerbook was never particularly good). On the other hand, a new PC card can bring 802.11g compatibility (54 Mbps up from 11 Mbps).
The other drawback to going non-Apple is the question over software compatibility. Most cards are aimed at Windows laptops and may not even support Macs. Even if Mac drivers are available, they are unlikely to be as cleanly integrated or as carefully debugged as the Apple drivers.
However, I read somewhere that the Belkin 802.11g cards were in fact compatible with the Apple AirPort drivers i.e. you could just plug them in and it would work. So I bought one for about $40 from J&R and plugged it in.
At first, it looked good - the software was offering me the option to turn on AirPort, but when I selected it, nothing happened. Eventually I just rebooted a few times and tried it a few times, and it started working, and has continued working ever since (I understand this only works with Mac OS X 10.2 with AirPort 3.1.1, or any version of OS X 10.3, which is what I am running).
When my second card died, I went out and bought another Belkin card, again from J&R. However, this card had different packaging and turned out to be a different version of the card - ver.3000 instead of ver.1315 like the first card I bought. This card is no longer based on the Broadcom chips, but instead uses "Ralink", and is not directly supported by the Apple AirPort drivers. Now, Ralink offers their own driver that you can download and install - I used it for a few weeks, and it works fine (it even offers some information not available under AirPort, like a list of all detected networks along with numerical signal strengths). But it's not as elegant - you have to run a separate program, there are typos - even in the menu bar of that program! And eventually, when I had to reinstall the OS after upgrading the hard disk, I had no easy way to download the drivers because, well, the network wasn't available!
So I looked on eBay. Most of the Belkin F5D7010 cards on offer didn't specify the version. Eventually I found one that was explicitly ver.1315, and bought it for cheap - $15 plus $10 shipping.
In my haste, I didn't read the advert very closely. Turns out the card was sold 'as-is'; judging from the packaging, it was a store return, and I soon found out why. Although it worked at first, it would just stop dead after a couple of hours, maybe because it was overheating. I don't know what to make of this, apart from (a) do be careful buying stuff on eBay - this is the second time I've ended up buying DoA stuff that way, and (b) the Belkin cards are pretty cheap, and maybe this is why - they can fail in insidious ways (although the original Apple cards aren't exactly stellar on this front either!).
Reading around, I learned that the Asante AL5403-XG 802.11g cards are also Broadcom-based and directly compatible with AirPort. When I searched for these (in mid-April 2005), I found them on sale, new, for $15, from Tigerdirect, via Amazon. I bought one straight off, and it arrived a few days later for under $20 including shipping! This card has been working great, and actually looks a little nicer than the Belkin - it doesn't stick out so far, which is a big plus. It's now happily working in our Pismo. The one working Belkin card is now in my Titanium Powerbook, and is also working great.
So, in summary;
The picture below shows the three different cards I've tried. The leftmost is the current Belkin F5D7010 (rev.3000), which needs a 3rd party driver to work on a Mac, which I don't recommend. The middle is the older Belkin F5D7010 rev.1315, which works, but has some reliability questions. The right is the Asante ALS5403-XG, my latest addition, which I recommend.