First, gaming over wifi is going to suck. Second, if you not getting a good signal it's likely that any adapter won't get a good signal unless you want to pay a good chunck of change for a high end one.
I've heard good things about powerline adapters, though I have no experience with them.
Newegg.com - TP-LINK TL-PA2010KIT AV 200Mbps Nano Powerline Adapter Starter Kit
I'm thinking about getting a set for my house too to go into my basement where the wifi isn't that good as well.