Networks looking for a sensitive wifi adapater

currently using the built in wifi on my ASUS board but even after buying a decent directional antenna, the onboard Realtek RTL8187 Wireless 802.11g card is just too crappy to give me a stable connection on the available wireless networks at my uni.

the majority of people with wireless built into their laptops can pick up a usable connection so I don't think I'll need a majorly expensive adapter, but I'd prefer something from one of the better companies, not just a generic dlink or buffalo adapter.

What are the current top brands when it comes to wifi range etc?

any suggestions would be greatly appreciated