Suggest a good macro lens for my Nikon D5100?

Can someone suggest a good & Not very expensive macro lens for my Nikon D5100?
I wanna do close up photography of water drops, spiderweb and such stuff.

There are screw-on "macro" adaptors on Ebay and at every flea market. Just find one that screws onto the front of your kit lens.

OR, for a real macro, consider the new Nikon 40mm AF-S Micro.
http://www.dpreview.com/...mmacro.asp

Tamron AF 18-270mm f/3.5-6.3 Di II VC LD Aspherical IF Macro Zoom Lens Featuring an incredible zoom range of 15x, the 18-270mm Di-II VC defines compositional versatility. Providing a 35mm wide-angle picture angle equivalent of 28mm to an astounding 419mm, image fidelity is assured in two ways