2.5" SSD in a 3.5" desktop drive bay normal?

I would just buy a 2.5" drive and use a mounting kit:

Now that they all use the same SATA ports, you just use the same standard connectors as any other hard drive.

Most SSDs tend to fit a 2.5" form factor, although there are some exceptions such as the OCZ Colossus. Adapters/brackets/mounting kits can be bought from most online computer stores. A Toshiba/Kingston SSD is one of the few drives that comes with a 3.5" adapter, but I wouldn't recommend the drive in terms of performance. I can't advise on the pros and cons of the different adaptors, as personally my SSD just "rests" in a 3.5" slot - there are no moving parts so I'm not that concerned about it.

Check out the ICY DOCK MB882SP-1S-1B 2.5" to 3.5" drive adapter.

http://www.newegg.com/Product/Product.aspx?Item=N82E16817994064

From what I know, you can use any laptop hard drives in a desktop, provided they are new enough that they use the SATA interface. No adapters should be needed, and it should rest nicely in your A: drive, floppy drive port.

It will also save you a little bit of power. but at the expense of a bit of speed. However, the 3.5 inch ssd's tend to cost a little more to buy. So, to recap

2.5 pros

1. lower power consumption
2. will fit the desktop, but won't sit tight unless you get a bracket to hold it in place
3. lower price

3.5 pros

1. faster speed
2. will fit nicely and screw in place