For your price cap(3k) you could get a great laptop and a very, VERY powerful desktop. I am not much on laptops but four, around 1.5k you can have a solid desktop that will work very well for years to come. There are some big things that will very your price, first is monitor real estate. You can usually find a very nice 22"+ refurb on new egg for 250-300. If you want two monitors, obviously it will cost more.
Also another thing to watch is on new egg they have combo deals that sometimes are really good, like right now they have a Phenom X6 3.2GHz Black Edition CPU, 700W cool master power supply, a GIGABYTE mobo with dual PCI express 1.0 and 2.0 slots so you can run duel graphics cards if you desire. A Cool Master mid tower, 4gb of DDR3 1866 ram( I personally would at least double that. The mobo can hold up to 16) a 1TB Seagate Baracude HDD and Cool Master cooler for the cpu. All for 608 dollars. So from there you NEED to add a disc drive, display(s), video card, and a mouse and a keyboard.
GPU:EVGA 02G-P3-1386-KR GeForce GTX 460 $219.99
Disc Drive:LG Black 12X BD-R 2X BD-RE 16X DVD+R 12X DVD-RAM 10X BD-ROM 4MB $99.99( or a standard dvd drive which would be cheaper)
good mouse of choice($50-$100)
keyboard of choice($10-$120)
Display:open boxSamsung B2330HD 23" 5ms Full HD HDMI WideScreen LCD Monitor w/TV Tuner & USB Port $199.99($399.98 for 2)
So without counting in the keyboard/mouse and only one monitor you are at a grand total of $1128.96 before shipping. That would easily leave you with $1600 to either get better(more expensive) parts or a really nice laptop.