It is risky right now, i wouldnt want to advise anyone as anything could go tits up.
Right now though if you have a few grand and fancy a gamble go for RBS, you could make a few hundred quid by tea time.
I am watching nexen though, their shares have fallen by 66% since july from $42 to about $15 now, which means the bigger fish, ie bp/ total will be sniffing round and looking to buy
It depends how long you can wait though