I was in your *EXACT* situation about 1 month ago, I had a 2405 as my primary display.
It's still a good monitor but I decided to ugprade to a 27" LED backlit HP unit. (2711x)
It has pros and cons, I remember spending 600+ on my Dell LCD back in the day, I didn't have that much to blow on an ultrasharp this time around so I had to be a bit more economical. The biggest diference is goin from 1920x1200 to 1920X1080p.
I don't know what your budget is but if its middle or lower you will be getting a 1080p monitor. Which is "okay" but to be honest I hate how the industry has for the most part followed suit with the TV industry and made 1080p the "popular" resolution. I'm used to gaming at 1920X1200.
All being said, I'm very happy with my purchase, comparing 6 year old display tech to what's new today is literally like night and day. The new LED backlit monitors are super bright and much thinner and lighter.
I picked up my 27" HP LED monitor from Fry's pricematched to newegg for 299.99 if your budget is more and you are looking at 24" sizes, you can get something pretty high end for 400-500 dollars that will likely last you another 6 years