Do not suggest him a $200-300 monitor if he's using a 20" Apple Cinema display - he's using a nice S-IPS panel monitor and every 24" under $400 is a TN panel which look horrible. Check viewing angles - 160 degrees is a TN panel, 170 is also TN. 178 degrees is a PVA or IPS panel and both are good. IPS offers more colour accuracy but lower refresh. If you want a mix of gaming and colour accuracy I suggest S-PVA. I'm currently using a Samsung 244T, not a currently new available monitor but it's an S-PVA 24" and I love it. Colour is wonderfully accurate, no nasty washout, no stupid shiny screen to glare, great brightness. You can pick up a refurb unit for $400-500 on eBay I believe (This monitor was $1,000 new, but if you're lucky you can find one used - I bought mine for $300).
However I'd look around - avoid Dell I've heard WAY too many people who had problems. I was going to buy a 2408wfp-hc but found WAY too many problems with their reliability and don't think it's worth the risk unless you find one super cheap. I recommend consulting this guide to determine what panels are in the monitor - trust me if you bought an Apple cinema display you won't be happy with a standard cheapo TN panel which is in all monitors under $400:http://lcdtech.no-ip.info/en/data/lcd.panels.in.monitors.htm
You may also want to look here for some up close comparisons of monitors:http://www.digitalversus.com/duels.php?ty=6&ma1=41&mo1=410&p1=3803&ma2=88&mo2=106&p2=1042&ph=8