I'm trying to run Bitcoin on a weak computer, which client consumes the least resources? I am running the standard client on a weak computer (Windows environment). It often is slow and unresponsive, and takes a noticeable chunk of the hard drive. I would want to replace it with some alternative client that offers the same functionality (mainly, running as server and supporting the standard Bitcoin API), while also consuming less system resources.

Which Bitcoin client consumes the least system resources and is the best fit for weak computers?
There is a very useful comparison of the Bitcoin desktop clients here:
http://dre.redmartian.org/compare.htm

In order 'lighter' to 'heavier' there are:

electrum

multibit

bitcoind

armory + bitcoind

If you need the full bitcoind RPC API then only bitcoind will do however. In that case trying/ waiting for v0.8 is probably your best option.