Ok, bridging isn't a big problem, I just needed to know what you meant. There are a couple of products I know of that do that very well, the first being Linksys' WET11. You plug your computer into it via ethernet, configure it via your browser, and it becomes a transparent part of the network.
As for something that acts like a wireless repeater, that's another issue. What works better is to have several access points connected by wired ethernet and configured for "roaming" access. That means that they all have the same network name (also called an SSID), but they're on different channels. When properly configured, your computer connects to the network through the access point with the best signal.
Some people feel that ethernet is a big problem to run through the house, or have concerns about how far an ethernet cable can go. The cable is smaller than a pencil, so it doesn't take a lot to run it through floors, ceilings, etc. (anyone who is generally capable of tying his or her shoes can get pretty good at attaching RJ45 connectors correctly in a very short time). The ethernet standard calls for supporting cable runs of up to 100 meters, so a few dozen feet within a house or between floors isn't a big issue.
My take is that trying to do what you want entirely with wireless will not only be extremely expensive (there are commercial wirele$$ repeater$) and difficult to put together, but a pain in the butt to configure and manage. Better to go the simpler, wired to wireless route.