There are a couple options, and the answer to the "is it worth it" question is basically, "yes" but depends on your configuration and needs, and only if you will be running windows 7 or better.
The fastest 6GB / sec SSD's will dramatically improve your boot, program load, and operations on your computer. There is no spinup or seek time. If you are constantly writing large files (saving music tracks from recording, working with large cad files, etc) then a SSD may not be the best way to go.
First off, there are a couple different things to consider with SSD's. not all SSD's are alike or even close. Some are glorified flash drives. Others are very very fast. Here are the main criteria
3GB per second or 6GB per Second:
Most existing motherboards and older SSD's have a maximum bandwidth of 3GB per second. this is fast, and faster than most rotational hard drives, but its not a huge amount faster. Some newer, high end motherboards now have 6GB / sec ports and some of the newest SSD's have 6GB / sec controllers. If you can pair that up you get a very, very very fast drive connection. A 120Gb 6GB / sec drive starts at $300 from newegg.
MLC vs SLC:
MLC, or Multi Layer Cell, refers to how the drive itself is constructed. SLC drives use just one layer of memory material per area ont he chip, and are therefore much faster and somewhat more theoretically reliable. MLC uses stacked layers, and have a bit of a speed penalty. The problem with SLC drives is you can't afford one. No one can. They exist only to torment us with listings of their awsomeness, and are otherwise mythical, like unicorns, or chimeras.
most Intel and corsair, and even most of the hated OCZ drives support the TRIM command. Some cheaper ones (and some older ones) don't, and its a huge issue. Essentially, when you delete something from a solid state drive, there are remnants left over that you dopn't encounter on a rotational hard drive. Eventually those build up over time and render your drive about 30% slower on average. the TRIM command cleans up those garbage elements and restores the drive to its initial speed. Windows 7 supports it, Windows XP kind of does if you hack in support via Intel tools. The latest Intel and Corsair SSD's have trim actually built into the drive so the OS isn't as big of an issue. Just make sure the drive supports TRIM.
Then there is the capacity issue. For gaming, you want all your operating system, your game files and any log files, etc on the same fastest drive. Assuming you want each of your games ont eh same drive, capacity becomes an issue. I personally haven't switched to a SSD yet because I need at least 220GB to transfer my existing OS partition over. Early drives were also hampered by an issue that you could not run SSD's in a Raid 0 array because TRIM would not function over a raid partition. Intel at least has since fixed that issue, so assuming you have a good amount of knowledge about setting up automatic system backups and imaging, you could run 2 drives in a raid 0, spanned, configuration. The upside is you essentially double the already fast speed of the SSD. the major downside is that if one drive fails, you lose your data on both drives.
Something else to consider are the Hybrid SSD drives that Seagate makes. The momentus XT series. They have a 4GB SSD and a 200-500GB rotational HDD paired together as a single unit. It plugs in like a normal hard drive, shows up as 1 drive in the system, but internally, things that are used most often and known heavy access files are stored in the SSD portion of the drive. less accessed data goes in the rotational portion. They aren't as fast as a good SSD, but they are faster than a 10,000 RPM raptor drive. I have one in my work laptop. I actually replaced my SSD because it was filling up too fast. I do notice a bit of performance loss, but its not much and not having to uninstall programs every time I want to go off site for longer than a day has been well worth it.