A few years ago, several experiments showed that laser-plasma accelerators can produce high-quality electron beams, with quasi-monoenergetic energy distributions at the 100 MeV level. These experiments were performed by focusing a single ultra-short and ultraintense laser pulse into an underdense plasma. Here, we report on recent experimental results of electron acceleration using two counter-propagating ultra-short and ultraintense laser pulses. We demonstrate that the use of a second laser pulse provides enhanced control over the injection and subsequent acceleration of electrons into plasma wakefields. The collision of the two laser pulses provides a pre-acceleration stage which provokes the injection of electrons into the wakefield. The experimental results show that the electron beams obtained in this manner are collimated (5 mrad divergence), monoenergetic (with relative energy spread <10%), tuneable (between 50 and 250 MeV) and, most importantly, stable.