A Labour/Lib Dem coalition doesn't look very likely at the moment - polls are running at about Con 37%, Lab 29%, Lib Dem 21%, which may translate to Con 300 seats, Lab 262, Lib Dem 55, others (mainly regional parties) 33. That would mean either a Conservative minority government, or a Con/Lib Dem coalition (they need 326 to get an absolute majority, so Labour + Lib Dem couldn't do that in that situation).
This site has a calculator to try to turn survey results into seat numbers, and tries to give the probability of various outcomes based around the surverys that have been taken.
http://www.electoralcalculus.co.uk/index.htmlThis site posts all the latest polls, with discussion (it's run by an employee of one of the polling companies):
http://ukpollingreport.co.uk/blog/If you really think a Lab/Lib Dem coalition is likely, you can get odds of 6/1 on it:
http://www.paddypower.com/bet?action=go_type&ev_class_id=33&disp_cat_id=56&ev_type_id=13104&ev_oc_grp_ids=239033