C/2007 W1 (Boattini):  

Keep an eye on this comet - it may reach 6th magnitude or better during early evening hours in late May before it gets too close to the Sun. See: http://cfa-www.harvard.edu/iau/Ephemerides/Comets/2007W1.html 

Looks like it'll actually get quite close to Earth but unfortuantely will be in the daytime sky at that point and so not viewable. :-(