An etext is a text that has been typed into a computer file and is thus SEARCHABLE.  Tens of thousands of Sanskrit texts have now been keyed-in, and are available to download for free from the web.  Here is a great index of Sanskrit etext archives.

Once a sizable etext archive has been downloaded, or better yet, obtained all at once from a colleague, one can search the whole corpus using a program with multi-file search capabilities such as the free and powerful TextWrangler (on MacOSX).  Windows users might try the freeware BareGREP, while Linux has it built in. It is often enough just to type in your search word without the ending (because of sandhi variation), but more refined searches can be easily accomplished with a search language called GREP.  For a helpful introduction on using GREP with Sanskrit etexts, see Somadeva Vasudeva’s brief exposition here.

I would like to echo Dr. Vasudeva’s plea concerning making your own etexts: it is not very time consuming when you consider the amount of time it takes simply to read a Sanskrit text and if you share your texts then the whole community of Sanskrit scholars benefits.  

I have so far produced the following etexts (click title for download link):

➤ Kāśyapīya Garuḍapañcākṣarīkalpa 
        (based on the 1933 ed. of Yatirāja Sampatkumāramuni)

➤ Nārāyaṇīya Tantrasārasaṃgraha
         (based on the 1950 ed. of M. Duraiswami Aiyangar)

I am also working on an etext of the Yogaratnāvalī, a composite work explicitly drawing on seventeen canonical Bhūta and Gāruḍa tantras.  It is slow-going as I only have copies of two corrupt manuscripts at my disposal.  I know of several other manuscripts scattered around India, but have not been able to obtain them yet.
http://indology.info/etexts/http://www.barebones.com/products/textwrangler/download.htmlhttp://www.baremetalsoft.com/baregrep/http://www.linfo.org/grep.htmlhttp://homepage.mac.com/somadevah/grep.htmlhttp://tantric-studies.org/e-texts/shaiva/GaPaKa.txthttp://tantric-studies.org/e-texts/shaiva/NaTaSaSa.txtshapeimage_2_link_0shapeimage_2_link_1shapeimage_2_link_2shapeimage_2_link_3shapeimage_2_link_4shapeimage_2_link_5shapeimage_2_link_6