Panel type 2.4 Ghz WiFi antennas can help you pull in wireless internet from up to a mile or more. One of the most discreet and tiny directional WiFi antennas is made by GSKY and sold with their powerful 500 mW wireless G adapter, seen here: Review Of The GSKY Long Range WiFi Adapter
You can see that this small antenna, which is about the size of a half a deck of cards, is very unobtrusive. It is shown in the photos with the review article, attached to a GSKY high power WiFi adapter. This powerful mini WiFi panel antenna has 7 dB of gain!
Works With Other High Power Wireless Adapters Too
I recently bought an Alfa 1 watt wireless adapter which is wireless B, G, and N capable. This puts out a full half watt more than the GSKY. Seen below is a photo of the Alfa 1000 mW wireless adapter. I will post a full review of the Alfa 1000 mW wireless adapter here on TheInfoMine soon. I am very pleased with this high power WiFi adapter and have found it to be even more powerful than the GSKY model I reviewed earlier. I tested it side by side on a hilltop overlooking a crowded subdivision in Austin and was able to pick up about 20 more wireless networks than the 500 mW GSKY. The fact that it is high speed wireless N capable is a big plus. I added the small, powerful WiFi panel antenna to the Alfa model and was able to pick up significantly more networks than with the included high gain omni antenna, and more than the GSKY adapter with the same mini WiFi panel antenna. You can also put this mini WiFi directional antenna on your router and beam WiFi toward a certain part of the house where you spend the most time. Using it on my Linksys router I gained another two bars in the living room. If your router has more than one antenna, just replace one of them with the panel antenna.
The compact directional WiFi antenna seen in that article is sold by itself and can be added to almost any router or wireless adapter with an RP-SMA connector (the most common kind of screw off router and adapter antenna).