Lens Mount Adapters . . . . . A cheap alternative or a waste of time ?

Just purchased my first DSLR . . .  an Olympus E 410 with a standard issue 17-45mm lens.  I have been on the lookout for a secondary lens but all the four third fitting lenses seem rather pricey considering I only paid £120 for the camera plus the original lens.

I then noticed lens adapters for Canon EF ,  M42 and others which are much cheaper plus have a larger choice.

The question is . . . . . .  pay top dollar for a four thirds lens or go for the adapter and a third party lens.

Stuart