Linksys WRT54GL is the way to go as it's only $50 after MIR from newegg. This particular model allows you to install 3rd party firmware to add more functionalities typically found in more expansive, enterprise level routers.
WRT54GL is just a linux based version of WRT54G with a bigger flash memory. With the current deal, you might as well get the WRT54GL for roughly the same price as the WRT54G.
As someone already mentioned, you shouldn't have connected your computer directly to the cable modem. A router will shield your computer from the internet with its stateful firewall.