Biggest problem with the Desire is its internal memory storage.
Rooting then using apps2sd+ is a fantastic solution.
The link posted above to Modaco is a great resource and a good starting point if you want to start getting in to custom ROMs.
You also have the benefit of a mature rooting guide now. When I had my Desire it was a proper hassle to root it.
There are a load of ROMs out there, I haven’t been following the Desire scene so not sure if Gingerbread is available yet. The Modaco roms are usually a good, safe and stable bet.
If you head over the xda-developers site there are loads more and its another great resource but also typically a little more technical.