There's lots of options, and plenty you could run in a jail. But you are on your own to install and use that software for the intended function. Most business have software that can often detect a configuration like you are trying to do, and many companies will terminate your employment as it's against their TOS.
There's far easier ways to get fired/quit if that's your intended goal.
Just to elaborate on this a bit.
If port 80 really is the only thing you have available, you'll be either proxying your sites in the clear, or trying to run SSL over the non-SSL port. Both of those are possible, but they'd raise red flags.
If instead, port 443 is also available for SSL connections (I find it hard to believe they're blocking all SSL) you could proxy over that and it would just look like a standard SSL connection. But, anyone that looks at your connections is going to notice that all your traffic is suddenly going to the same IP. Again, red flag.
Is it really that important that you get to these sites? If they're legitimate, just ask that they be unblocked. If they're not, get back to work ;-)