Low space on HTC Desire with CyanoGenMod 7.1: how to solve it?
Many ways lead to rome:


Try a ROM that specifically fixes your problems: I use an ICS build, Sandvold's ICS for Desire which comes with 4 different App2SD methods included (XDA thread) which I find rather stable. You can have a look over to XDA's Desire forum, to search for more roms.
Use Link2SD, create a 2nd ext2/ext3/ext4 partition that a choice of your apps get moved to (manually) and symlinked from /data/ to. See app on Google Play, official FAQ.
CM7 also supports the standard move to sdcard method that you can also use (and might already be aware of. Downside: /data get's full anyway really soon)
You could try to flash a different bootloader (called hboot on desire, that has another partition layout. See Alpharev for instructions and downloads, there's data++ with 180MB and cm7r2 with close to 300MB free for apps at the expense of shrinking other partitions (/system, /cache/, ...). Not every ROM fits all of these though. WARNING: Not for the faint hearted! Read about the risks!