As I've mentioned in the past, the single best way to improve Internet performance in your home is to plug your PC directly into your router. After that, the best bang for the buck comes from ditching your old 802.11g router in favor of an 802.11n model.
And you don't need a lot of bucks to do that. Newegg has the D-Link DIR-601 802.11n wireless router for $19.99 shipped. That's after adding it to your cart and applying coupon code EMCKBGK58 at checkout.
The benefits of 802.11n are numerous and well-documented: faster throughput, better range, and stronger security options. Your mileage can and will vary depending on things like the size of your house, placement of the router, and so on. But speaking from personal experience, 802.11n blows 802.11g out of the water.
The DIR-601 is a single-band router with four 10/100 Ethernet ports, an external antenna, and a one-year warranty.
The user reviews for this model are all over the place, as they are with virtually every Wi-Fi router I've seen. Sometimes people don't follow setup instructions, sometimes there are "environmental" issues like the ones mentioned above, and sometimes you just get a bum unit. But overall, the ratings are fairly solid.
My take: For $20, it's hard to go wrong--especially if you're still living with an old 802.11g router.
Bonus deal: Amazon is once again offering a $5 Amazon Instant Video credit when you link to your Twitter account. If you nabbed this deal last time, you can sign into your Twitter account, revoke Amazon's access, and then link again.