What speakers are suitable for connecting to a TV?

To be perfectly technical, none. :D

Okay, this may sound wery 'what the hell?'ish. In practice, the TV puts out the amplified signal into its speakers, and if it has an audio-out jack/2xRCA, that output is signal-level, which is to say, NOT amplified.

So, long story short - you need an amplifier to go with the speakers. Otherwise the signal would be so small that you wouldn't hear anything! But this simplifies things considerably: sets of amplifier+speakers are available in almost every major electronics/RTV store, and they're pretty much guaranteed to work with signal-level input (that's what design standards are for). So go ahead and buy a set of speakers with a matching amplifier, and it should work like a charm.