Here's what the Google AdWords: Keyword Tool sees as the highest-priced keywords related to "proxy":

Keywords Estimated Avg. CPC
web proxy servers $6.91
free web proxy $4.83
web proxy server $4.06
web proxy $3.49
proxy filter $2.71
ssl proxy $2.56
proxy websites $2.36
anonymous web proxy $2.33
proxy software $1.97
proxy host $1.95
firewall proxy $1.93
fast proxy server $1.76
https proxy server $1.76
linux proxy $1.75
school proxy $1.65
anon $1.61
smtp proxy $1.54
proxy website $1.47
online proxy server $1.45
proxy server $1.43
proxy severs $1.37
socks $1.36
buy proxy $1.35
proxy port $1.28
free proxy $1.26
proxy services $1.18
proxy server address $1.18
reverse proxy $1.15
proxy+ $1.15
anonymous web $1.07
proxy $1.06
internet proxy $1.06
squid proxy $1.05
browser proxy $1.05
the proxy $1.03
ftp proxy $1.02
web based proxy $1.02
healthcare proxy $1.01
anonymous proxy server $0.99
proxy server download $0.96
anonymous $0.95
anonymus $0.93
proxy server list $0.93
proxy scanner $0.91
proxy finder $0.90
anonymous proxy server list $0.90
proxy servers $0.89
proxy server ip $0.87
transparent proxy $0.87
url proxy $0.87
public proxy server $0.86
proxy com $0.86
fast proxy $0.86
proxy sites $0.85
orkut proxy $0.83
anonym $0.83
privacy proxy $0.82
proxy site $0.81
public proxy servers $0.81
secure proxy $0.79
new proxy $0.78
free proxy server $0.77
anonimous $0.76
8080 $0.76
proxy cache $0.75
www proxy $0.74
squid cache $0.74
proxy anonyme $0.73
no proxy $0.70
socks 5 $0.69
ergo proxy $0.68
socks proxy $0.68
web proxy service $0.67
cgi proxy $0.66
sock proxy $0.66
irc proxy $0.66
proxys $0.64
http proxy $0.64
socks5 $0.64
proxi $0.63
anonymous proxy $0.63
proxy address $0.63
online proxy $0.62
anonymous web surfing $0.61
free proxies $0.61
open proxy $0.61
proxy checker $0.60
proxy search $0.58
bypass proxy server $0.57
anonymity $0.57
anonymous web surfing proxy $0.56
free proxy servers $0.55
anonymous proxy list $0.55
proxylist $0.55
proxy 3128 $0.54
proxy liste $0.52
free proxy list $0.51
proxies $0.49
proxy service $0.48
anonymous surfing $0.47
proxy servers list $0.46
socks4 $0.46
https proxy $0.45
proxy bypass $0.45
anonymous internet proxy $0.45
free anonymous proxy $0.44
anonymous proxy servers $0.44
3128 $0.44
ip proxy $0.44
public proxy $0.44
proxie $0.43
proxy list $0.43
proxy surfing $0.43
phpproxy $0.42
surf anonymously $0.42
anonymous proxies $0.41
anonymous proxy sites $0.40
multiproxy $0.40
proxy ip address $0.39
anonym proxy $0.39
proxy anonymous surfing $0.38
whois proxy $0.37
free proxy sites $0.36
phproxy $0.36
anonymous proxy browsing $0.35
anonymous proxy surf $0.34
proxy lists $0.32
proxify $0.32
elite proxy $0.31
fire proxy $0.31
anonymous surf $0.31
proxy proxify $0.30
proxy surf $0.29
socks5 proxy $0.28
anonymous ip $0.28
multi proxy $0.27
anonymity proxy $0.26
anonymous proxy browser $0.25
high anonymity $0.24
anonymous proxy ip $0.22
proxify anonymous proxy $0.22
fresh proxy list $0.21
anon proxy $0.20
high anonymity proxy $0.18
alive proxy $0.18
proxy codes $0.16
proxy anonimous $0.16