Generally I've had very good luck with Toshiba laptops. They don't offer much in the way of fancy bells and whistles, but they don't come with high prices, either, and I'm good with that. Unfortunately, this latest one I have, the S855-S5254, has really had some issues with wireless network connectivity recently.
As I tend not to think it's the laptop, I've been racking my brain trying to figure out the problem. Our cable was cut, so I have been on the phone with Time Warner trying to see if they would come out and check it (they won't, they already came out and re-buried the line). So I bought a new D-Link router, and a Netgear one, to replace the venerable Apple Airport that we have. After spending who knows how long trying to get things reconfigured, and watching the time graph of inSSIDer on multiple devices, it seems the problem is the laptop. Wonderful.
Luckily, most Toshibas are easy to upgrade. Just pop a panel on the bottom and replace the component - memory being the most common. In many cases, however, you may want to add another hard drive or, as is the case here, replace the wireless card (the model for this laptop is the RealTek RTL8723AE Wireless Lan 802.11n PCI-E NIC). The first problem is that this model doesn't seem supported by anyone, be it Realtek or Toshiba, and there are complaints everywhere.
Unfortunately, the bottom panel doesn't give you access to the wireless card. The next most common location is to look under the keyboard - usually by careful removal of a small panel at the top of the keyboard, which gives you access to some screws which can then allow the keyboard itself to come loose. In this case, however, no such screws are necessary. You can just pry the keyboard out (carefully!), and then get underneath it. Unfortunately, no access to components is underneath the keyboard.
On to the next step: Start removing screws from the bottom of the case. What seems like dozens of them. Once that is done, carefully start prying loose the case from the chassis, being careful not to break anything in the process. You'll also want to remove the battery and the memory access panel, because there are even more screws hidden under those. You also need to take out the hard drive, because it helps hold things in place. I am serious - we're talking a lot of screws. Make sure you are someplace that you don't lose these screws. I started on the couch and rapidly changed locations when screws started rolling everywhere.
Finally, you'll have access to the network card. When looking at the bottom of the laptop, with only the panel removed, there is a small circular opening that looks like it's a good spot for the CMOS battery, but there is no battery there. That's actually the edge of where the card goes - but you can't get to it without removing all these screws I'm talking about. Someone needed to plan this thing better.
The next step is to replace the card. I scavenged old laptops to look for one. Now this card is tiny - about an inch by an inch and a quarter. It's called a "PCI-E", or PCI-Express card, but there doesn't appear to be a standard form factor for this, size-wise.
Luckily, there is some room to work with on the length. I had one that fit the socket, but was too long, and that had an extra antenna (this card only has two). I then found another that fit, and had the right number of antennas. The only problem was that I had to stretch the antenna wires a bit - the new card was one and a half inches long.
So it fit, but just barely. In fact, it's now sitting on top of a capacitor, which I don't think is a problem, but I am keeping my fingers crossed. It also doesn't screw down, but the case is pretty tight, so I don't think that's an issue. It also came from a Toshiba, which made me feel better. The particular model is an Atheros AR5006EG, and you can find them for about $4 online, if you don't have another unit to scavenge like I did. This one offers only 802.11b and g, but it doesn't drop the signal nearly as often as the RealTek, which is a pleasant change. I'll trade consistent connection for a bit of top-end speed any day.
Once you're done, find all those screws and carefully put things back together and you should be good to go. When you start back up, the new card may be recognized automatically. If not, you might need some drivers for it. Hopefully you got those before starting, right?