There's a lot to be said for getting an iMac - it can do what you need (probably - based on your brief description). But if you have a nice monitor and don't particularly see how having two monitors would be of significant benefit then I think you might seriously consider this MacPro refurb:
http://store.apple.com/1-800-MY-APPLE/We...=FB052LL/A
It's a $100 more than the top-of-the-line iMac but its got so much more:
Two 3.0GHz Dual-Core Intel Xeon processors
2GB [4 x 512MB] memory (667MHz DDR2 fully-buffered DIMM ECC)
250GB Serial ATA 3Gb/s 7200-rpm hard drive
Two 16x SuperDrives (DVD+R DL/DVD±RW/CD-RW)
ATI Radeon X1900 XT graphics with 512MB memory
Notice that it has two SuperDrives and a really nice graphics card. It's incredibly easy to add ram and hard drives to that machine. And I can't imagine that it won't hold its resell value way more than the iMac. It is the previous generation of MacPro, but I don't think the new ones are significantly more capable than that one unless you are doing something like heavy duty video work.
If you are looking at the 2.8Ghz 24" iMac for $1800 then there isn't much of any Mac Pros in that price range; although you might consider this one for $2000:
http://store.apple.com/1-800-MY-APPLE/We...=FA356LL/A
Two 2.66GHz Dual-Core Intel Xeon processors
1GB [2 x 512MB] memory (667MHz DDR2 fully-buffered DIMM ECC)
250GB Serial ATA 3Gb/s 7200 rpm hard drive
16x SuperDrive (DVD+R DL/DVD±RW/CD-RW)
NVIDIA GeForce 7300 GT graphics with 256MB memory