Since version 3.3 Python has his own virtual environment build-in. This is extremely useful especially if you like to install development or other specific versions of python libraries without messing with Ubuntu's repository python libs.
Sadly it is broken in Ubuntu 14.04 and 14.10. If you try:
sr4l@LARS-Laptop:~$ pyvenv-3.4 myvenv
Error: Command '['/home/sr4l/myvenv/bin/python3.4', '-Im', 'ensurepip', '--upgrade', '--default-pip']' returned non-zero exit status 1
sr4l@LARS-Laptop:~$
You can only use it without pip and later install pip manually. (Bug report)
With Ubuntu 14.04s Python 3.4 and the newest version of setuptools and pip:
# create python venv in folder myvenv without pip
pyvenv-3.4 --without-pip myvenv
# enter the venv
source ./myvenv/bin/activate
# download, extract and install (in venv) setuptools
wget https://pypi.python.org/packages/source/s/setuptools/setuptools-7.0.tar.gz
tar -vzxf setuptools-7.0.tar.gz
cd setuptools-7.0
python setup.py install
cd ..
# download, extract and install (in venv) pip
wget https://pypi.python.org/packages/source/p/pip/pip-1.5.6.tar.gz
tar -vzxf pip-1.5.6.tar.gz
cd pip-1.5.6
python setup.py install
cd ..
# leave the python venv
deactivate