I've been using PopTray to keep an eye on 4 different accounts and its worked great for me. Includes simple "rules" processing as well.

As mwb1100 mentioned, I was also having a lot of problems with my WRT54G locking up occasionally (actually way too often). After flashing the "DD-WRT micro" firmware into it, mine has been performing flawlessly as well.  I highly recommend it, the VxWorks firmware that LinkSys has gone over to is garbage.  Just remember that there is a small risk of "bricking" your router if you don't do a little homework first and follow directions exactly when flashing alternate firmware.  It's a good idea to have a backup router so if your main box dies you're home network isn't down while you rush out to buy a replacement (I just picked up a wireless/wired TP-Link TL-WR340G off ebay, they're going for $20 and seem quite capable). Also if you're going to put all your files on a central server, figure out what your file backup strategy will be up front so that you can plan your hardware accordingly, hard drive space is so cheap nowadays. I've been using SyncBackSE to cross backup critical directories from each machine to one of the other 3 machines on the network, that way if a drive or motherboard dies the files are instantly available on another pc.  This combination of things has worked well for my home network, without having to spend much $, and with nearly 100% up-time.