My suggestion is a Western Digital Caviar 120GB IDE 7200RPM
Special Edition 8MB cache WD1200JB! You get smaller Hds from the same brand, either with less space or less cache, but then again the price is cheaper!
If you want speed at an affordable price, go with the IBM GXP 120 available in 5 different sizes up to 120G. Can be gotten for around $100.00 in the 60G size on-line. I have had hard drive scores of 1200+ on PCMark 2002 running ATA-100 with XP Pro. I know earlier GXP's have had some problems but the GXP 120's have been true performers.